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Copyright^ . 



COPYRIGHT DEPOSIT. 




Fig. I. 



Convex Surface of Cerebrum Cortical Areas. 




Fig. II. 
Cortical Areas on Medial Surface of Cerebrum. 



ANATOMY 

OF THE 



Brain and Spinal Cord 

WITH SPECIAL REFERENCE TO 

THE GROUPING AND CHAINING OF NEURONES 
INTO CONDUCTION PATHS. 

For Students and Practitioners. 



BY 

HARRIS E. SANTEE, M. D, Ph. D., 

M 
Professor of Anatomy in The College of Physicians and Surgeons, 
Medical Department, University of Illinois ; Professor of 
Anatomy in Harvey Medical College, Chicago. 

WITH A PREFACE BY 

WILLIAM T. ECKLEY, M. D., 

Professor of Anatomy in the Medical and Dental Departments, 

University of Illinois. 



SECOND EDITION 
REVISED AND ENLARGED. 



Chicago : 

E. II. COLEGROVE 

1902. 



A 



.^ 



THE LI8RARY OF 
GOW3RESS. 

~'vr> Ci>P<tS ReCKIVED 

SEP. 15 1902 

OOPVPIOHT EHTWV 

CUASS A^KXo. Mo. 
COPY 3. 



Copyright, 1902, by Harris E. Santee, 
Chicago, III. 



P E E P A C E . 

It is with pleasure I respond to the author's invitation to 
•write an introductory page, and I sincerely acknowledge the 
compliment. 

My remarks, necessarily few, are in the nature of convic- 
tions founded on a study of this and the previous edition, on 
a comparison of this work , with others of similar nature, on 
a long personal acquaintance with the author, an appreciation 
of his conception of anatomy and his methods of teaching 
the same. To peruse the book, is to convince one of its value 
as a contribution to our literature ; to know the author, is to 
enhance the desirability of the book. 

It is needless to comment on detail, logical arrangement 
and orderly subordination of minor to major parts, looking 
to the ultimate desideratum of a monograph on the brain and 
spinal cord, for the use of students and practitioners. Such 
features are possessed by books in general. My remarks will 
be directed to what I consider superior qualities, these inci- 
dentals which relieve the tedium of scientific detail and in- 
delibly impress the practical value of a subject. 

The composition, relation and contour of the operculum 
and posterior part of the inferior frontal gyrus, become more 
interesting, when it is shown that "They constitute (he re- 
gion of speech." In like manner, that "The temporal lobe 
is the probable seat of the centers of taste, smell and hear- 
ing," and that "The ascending frontal, ascending parietal 
and superior parietal convolutions are the best known motor 
areas of the cortex," are physiological observations which 

in 



PREFACE. 

instruct and fascinate alike. In this manner, throughout 
the book, the author invokes function of a region to gain an 
anatomical end. 

The olfactory lobe in man, represented by the bulb, tract, 
trigone, area of Broca and anterior perforated space, finds 
the lobar antecedent and a reason for its name, in the lower 
animals, and in this way the author elucidates a point whicb 
were incomprehensible to the student without such compari- 
son. 

The adult human brain is complex, stable, coherent and 
heterogeneous, but as a simple, comprehensible means to a 
great teaching expedient, the author invokes the precepts of 
embryology to show that this composite brain had a simple 
vesicular prototype whose simple cavity became complex ven- 
tricles, whose simple spongioblasts became complex neu- 
rogiiar network, whose simple primitive neuroblasts became 
neurones, with cell-bodies and dendrites in cortex and ganglia, 
and medullated axones forming the white substance of the 
brain. 

Numerous illustrations might be drawn from every chap- 
ter of the book to show like superior teaching qualities, but 
observations which even the most casual perusal of the book 
itself makes apparent add nothing of value to criticism. 

In his presentation of the tracing of impulses, Dr. Santee 
has done more to simplify the complex conduction paths to 
and from the brain than any author after whom I have read. 
In this respect his book excels, and must appeal to teachers 
of anatomy, practitioners of medicine and students alike. 

The conception of a motor nerve according to many is a 
tangible band of white matter (as the anterior tibial) asso- 
ciated above with a plexus. Dr. Santee's conception, how- 
ever, is a path composed of numerous neurones extending 

IV 



PREFACE. 

from a cortical area in the neighborhood of the Kolandic 
fissure through the pyramidal tracts of the spinal cord to both 
co-ordinated and inco-ordinated muscles. His conception of 
a sensory conduction path is not the ordinary one which 
leaves the student in doubt as to the location of trophic cells 
of centripetal nerves, but the embryological one which recog- 
nizes sensory spinal and sensory cranial nerves as growing 
toward and into the brain, from posterior root and cephalic 
ganglia respectively. Such a conception of motor and sen- 
sory nerves enables a student to read intelligently the de- 
generations. Again, it is superior teaching that ascribes 
function to the definite tracts of fibers, to- wit: "The pyram- 
idal tracts are motor;" "Gower's tract probably carries 
thermic and pathetic impulses;" "Golfs column carries im- 
pulses of the muscular sense;" "All varieties of impulse are 
carried by Burdach's column;" "The direct cerebellar tract- 
conveys impulses of equilibrium received especially from the 
viscera." 

In conclusion, Dr. Santee's "Anatomy of the Brain and 
Spinal Cord" is concise, exact, scholarly, and possesses su- 
perior qualities in the manner of elucidation; it gives the 
most comprehensive exposition of the conduction paths of 
the brain and spinal cord of any book in our language, and 
is destined to become popular everywhere. 

Very truly, 

W. T. ECKLEY. 



CONTENTS. 
Chapter I. 

PAGE. 

Membranes of the Brain 1-6 

Dura Mater 1-4 

Middle meningeal artery 3 

Arachnoid 4-5 

Pia mater 5-6 

Table 1. Grand divisions of brain 6-7 

Chapter II. 

The Cerebrum 8-51 

Section i. 

Exterior surface 9-24 

Convex surface 9-14 

Fissures 9-11 

Lobes and convolutions 11-14 

Medial and tentorial surface 14-17 

Fissures 14-16 

Lobes and convolutions 16-17 

Basal surface 17-24 

Medial structures 18-21 

Lamina cinerea 18 

Tuber cinereum 18 

Pituitary body 19 

Corpora albicantia 19 

Optic commissure 20 

Lateral structures 21-24 

Orbital lobe 21 

Island of Reil 22 

Olfactory lobe 22 

Section 2. 

Interior surface of cerebrum 24-51 

Internal capsule 25-28 

VII 



CONTENTS. 

PAGE. 

Corpus callosum 28-30 

General cavity of cerebrum 30-31 

Fornix 32-33 

Septum lucidum 33 

Fifth ventricle 33-34 

Lateral ventricle, body 34-42 

Corpus striatum 35-37 

Taenia semicircularis 37 

Optic thalamus 37 

Choroid plexus 38 

Cornua, anterior, posterior and middle 38-42 

Third ventricle 42-43 

Boundaries 43-44 

Roof epithelium 44-45 

Pineal body 45-46 

Velum interpositum 46-47 

Choroid plexus and tela 46 

Anterior commissure 47 

Optic thalamus 48-50 

Hypothalamic region 50 

Geniculate bodies, external and internal 50-51 

Chapter III. 

The Mid Brain 52-65 

Surfaces 52-54 

Interior 54-65 

Crustae 54-56 

Intermediate bundle 55 

Temporal cerebro-corticopontal tract 55 

Pyramidal tract 55-56 

Frontal cerebro-corticopontal tract 56 

Substantia nigra 56-57 

Tegmentum 57-65 

Aqueduct of Sylvius 58 

Corpora quadrigemina 59 

Internal geniculate body 60 

Fibers of tegmentum 60-65 

Posterior longitudinal bundle 61 

VIII 



CONTENTS. 

PAGE. 

Anterior longitudinal bundle 62 

Fillet or lemniscus 62-63 

Superior peduncle of cerebellum 64 

Olivary bundle 64 

Tract from red nucleus 65 

Chapter IV. 

Gray and White Matter of Cerebrum and Mid Brain.. 66-99 

Neurone 66-70 

Sustentacular tissue 67 

Cortical gray matter 70-76 

Motor areas 70-71 

Somassthetic area (common sensory) 70 

Special sense areas . .• 71 

Association centers 71-72 

Effect of lesions in special areas 72 

Layers of typical cerebral cortex 72-74 

Exceptions 74-76 

Ganglionar gray matter 76-84 

Corpus striatum 76-78 

Caudate nucleus 76 

Lenticular nucleus 76 

Lesions in corpus striatum 77 

Optic thalamus 78-81 

Nuclei of thalamus 78-79 

White matter of thalamus 79-80 

Lesions of lateral nucleus and nucleus of pulvinar 78 

Nucleus hypothalamicus (Luysi) 81 

Nucleus ruber (red nucleus) 81 

Geniculate bodies 82 

Corpora quadrigemina 82-83 

Substantia nigra 83-84 

Central, or ventricular, gray matter 84-85 

Lamina cinerea and tuber cinereum 84 

Middle commissure (massa intermedia) 84 

Nuclei of oculomotor and trochtear nerves S4 

Projection fibers— Motor 85-89 

Internal capsule and crusta 85-89 



CONTENTS. 

PAGE. 

Pyramidal tract 86-89 

Cranial fibers .87 

Upper extremity fibers 87 

Trunk fibers 88 

Lower extremity fibers 88 

Frontal cerebro-corticopontal tract 86 

Temporal cerebro-corticopontal tract 86 

Intermediate bundle 86 

Tegmentum 88 

Descending tract from red nucleus 88 

Anterior longitudinal bundle 88 

Lesions of motor tracts 89 

Projection fibers — Sensory 89-91 

Tegmentum 89 

Internal capsule — common sensations 89-91 

Three systems of Flechsig, or cortical fillet 89-90 

Ansa peduncularis 89 

Ansa lenticularis 89-90 

Anterior stalk of thalamus 90 

Lesions of cortical fillet 90 

Internal capsule — special sensations 90-91 

Acustic radiations 90 

Optic radiations 90-91 

Lesions of acustic and optic radiations 90-91 

Commissural fibers 91 

Corpus callosum 91 

Anterior commissure 91 

Lyre, or commissura hippocampi 91 

Association fibers 91-94 

Short 91 

Certain lesions of 92 

Long 92-94 

Cingulum 92 

Fornix 92 

Uncinate fasciculus 93 

Lesion of , 93 

Superior longitudinal fasciculus 93 

Interruption of 93 

x 



CONTENTS. 

PAGE. 

Inferior longitudinal fasciculus 93 

Fasciculus occipito-frontalis 93 

Perpendicular fasciculus 94 

Blood supply of cerebrum and mid-brain 94-99 

Cortical system of arteries 95-96 

Ganglionar system of arteries 96-97 

Veins 98 

Lymph spaces 99 

Chapter V. 
Hind Brain 100-128 

Section i. 

Cerebellum 100-118 

Functions 100 

Hemispheres and vermis 100-101 

Medullary vela 101-102 

Cerebellar peduncles 101-103 

Superior surface 103-107 

Fissures and lobes 103-107 

Inferior surface 107-111 

Fissures and lobes 107-111 

Interior 111-118 

Gray matter 111-114 

Cortical 111-113 

Functions and lesions of 113 

Ganglionar 113-114 

White matter 114-118 

Projection fibers 114-116 

Cerebellar peduncles 114-116 

Commissural fibers 116 

Association fibers 117 

Blood supply 117-11S 

Section 2. 

Pons 118-128 

Surfaces 119-120 

White matter of Pons 120-125 

XI 



CONTENTS. 

PAGE 

Transverse fibers 121-122 

Ventral 121 

Middle 121 

Dorsal 121-122 

Longitudinal fibers 122-125 

Ventral (pyramidal) 122 

Middle (formatio reticularis) 123 

Fillets 123-124 

Posterior longitudinal bundle 124 

Anterior longitudinal bundle 124 

Olivary bundle 124-125 

Tract from red nucleus 125 

Root of trifacial nerve 125 

Dorsal longitudinal fibers 125 

Superior cerebellar peduncles 125 

Valve of Vieussens 125 

Gray matter of pons 126 

Nuclei pontis 126 

Nuclei of formatio reticularis 126 

Cranial nerve nuclei 126 

Superior olivary nucleus 126 

Lesions of pons 127 

Blood supply of pons 127 

Chapter VI. 

Medulla Oblongata , 128-149 

Surfaces 129-133 

Ventral 130-131 

Lateral 131-132 

Dorsal 132-133 

Interior — white matter 133-145 

Formatio reticularis and raphe 134-135 

Transverse fibers 135-136 

External arciform anterior and posterior 135 

Internal arciform 136 

Sensory, or fillet, decussation 136 

Cerebello-olivary tract 136 

Dorso-ventral fibers — nerve roots 136-137 

XII 



CONTENTS. 

PAGE. 

Longitudinal fibers 137-145 

Pyramids 138 

Formatio reticularis alba 138-139 

Interolivary fillet 139 

Posterior and anterior longitudinal bundles. .139-140 

Formatio reticularis grisea 140-141 

Antero-lateral ground bundle 141 

Triangular tract (Helwig) 141 

Antero-lateral cerebellar tracts 141-142 

Tract from red nucleus 142 

Fasciculus gracilis 142-113 

Fasciculus cuneatus 142-143 

Fasciculus Rolandi 143-144 

Direct cerebellar tract 144 

Restiform body 144-145 

Fasciculus solitarius 145 

Fasciculus teres 145 

Interior — gray matter 146-149 

From anterior horn 146-147 

From posterior horn 147 

Added nuclei 147 149 

Lesions of medulla 149 

Chapter VII. 

Fourth Ventricle 150-158 

Boundaries 150-153 

Eminentia teres 151-152 

Fovea superior 151-152 

Locus coeruleus 151-152 

Trigonum hypoglossi 152 

Trigonum vagi 152-153 

Trigonum acustici 152 153 

Table II. Origins of cranial nerves 153-158 

Ventral nuclei, motor 156-157 

Dorsal nuclei, sensory 157-158 

Blood supply of medulla oblongata 158 

Chapter VIII. 

Meninges of Spinal Cord 159-161 

Dura mater 159 

XI 1 1 



CONTENTS. 

PAGE. 

Arachnoid 160 

Pia mater 160-161 

Ligamentum denticulatum 161 

Nerve and blood supply 161 

Chapter IX. 

The Spinal Cord 162-184 

Enlargements of cord 163 

Ventricle of cord 163 

Surface 163-165 

Fissures 163-165 

Gray matter of cord 165-171 

Substantia gelatinosa 166 

Substantia spongiosa 166 

Anterior horn of crescent 166-168 

Lesions of 167-168 

Center of crescent 168-169 

Posterior horn of crescent 169-170 

Gray commissure of cord 170-171 

White matter of cord 171-182 

Anterior commissure 171-172 

Nerve roots 179-182 

Tracts (longitudinal) 172-179 

Ascending 172 

Descending 172 

Mixed (ascending and descending) 173 

Antero-lateral ground bundle 173-174 

Anterior and posterior longitudinal bundles. .173-174 

Uncrossed (direct ) pyramidal 174 

Antero-lateral descending cerebellar 174 

Antero-lateral ascending cerebellar 175 

Triangular (Helwig) olivary of cord 175 

Direct cerebellar , 175-176 

Crossed pyramidal 176-177 

Crossed descending from red nucleus 176 

Lesions of pyramidal tracts 177 

Marginal (Lissauer) 177 

Postero-lateral (Burdach) 177-178 

XIV 



CONTENTS. 

PAGE. 

Cornu commissural 178 

Septo-marginal 178 

Comma 178 

Postero-median (Goll) 179 

Lesions in posterior columns 179 

Roots of spinal nerves 179-182 

Anterior roots 180 

Origins — superficial and deep 180 

Lesions of lower motor neurones . 180 

Posterior roots 180-182 

Central terminations 181 

Superficial (apparent) 181 

Deep (real) 181-182 

Lesions of posterior roots 182 

Blood supply of the cord 182-184 

Chapter X. 

Tracing of Impulses 185-201 

Efferent, or motor, paths, through 185-190 

Pyramidal tracts 185-186 

Frontal cerebro-corticopontal tract 186-187 

Temporal cerebro-corticopontal tract 187 

Intermediate bundle 187 

Red nucleus — direct and indirect 188 

Short fiber paths (formatio reticularis) 188-190 

Facial paralysis, nuclear and nerve trunk 189 

Abducent paralysis and irritation 189-190 

Afferent paths, general sensation 190-193 

Columns of Goll and Burdach 190-192 

Direct 190-191 

Indirect 191-192 

Cranial nerves and medial fillet 191 

Direct cerebellar tract 191-192 

Antero-lateral ascending cerebellar tract 192-193 

Short fiber paths (antero-lateral ground bundle).... 193 

Lesions of sensory tracts. . 193 

Afferent paths, special sense 194-197 

Olfactory 194 

XV 



CONTENTS. 

PAGE. 

Optic 194-195 

Auditory 195-197 

Cochlear 195 

Vestibular 196 

Gustatory 197 

Lesions of special sense tracts 197 

Reflex paths 198-201 

Varieties of reflex arcs 198 

Spinal reflexes 198-199 

Defecation, etc 198-199 

Cranial reflexes 199 

Spinal and cranial reflexes 199-200 

Cranial and spinal reflexes 200-201 

Respiratory 200 

Auditory 200 

Pupillary 2OO-201 

Chapter XL 

Embryology of Brain and Spinal Cord 202-224 

Neural crest 202-204 

Cranial nerve ganglia 202-203 

Spinal and sympathetic ganglia 203-204 

Neural tube 204-224 

Three histologic layers 205 

Neurogliar 205 

Mantle 20") 

Ependymal 205 

Flexures 206 

Table III. Brain vesicles and derivatives 207-208 

1. Prosencephalon 208-213 

Hemisphere vesicles 208-213 

Foramen of Monro and lateral ventricles. 208 

Olfactory lobe 208 

Fissures, primary and permanent 209-210 

Special thickenings .210-211 

Fusion of Hemispheres with one another. . 211-212 

Fusion with thalamencephalon 212 

Velum interpositum 212-213 

XVI 



CONTENTS. 

PAGE. 

2. Thalamencephalon 213-214 

Optic vesicle 213 

Thalamus 214 

External geniculate body 214 

Posterior commissure 214 

Pineal body 214 

3. Mesencephalon 214-215 

Tegmentum 215 

Corpora quadrigemina 215 

Internal geniculate body 215 

Aqueduct of Sylvius 214 

Substantia nigra 215 

Crustae 215 

4. Epencephalon 215-216 

Cerebellum 215-216 

Vermis 216 

Hemispheres 216 

Penduncles 216 

Pons 216 

Nuclei of pons 216 

Nuclei of cranial nerves 216 

5. Metencephalon 217-219 

Internal surface 218 

External surface 218 

Three histologic layers 218-219 

Ependymal 218 

Mantle 218-219 

Neurogliar 219 

Spinal cord 220-224 

Ventral and dorsal zones 220-221 

Histologic layers 221 

Mantle layer — gray substance 221-222 

Tracts of fibers— when medullated 222-223 

Fissures of cord 223-224 



XVII 



CHAPTEE I. 



THE MENINGES OF THE BRAIN. 1 

Three membranes invest the brain and spinal cord. They 
are, from without inward, the Dura Mater, the Arachnoid, 
and the Pia Mater. Each membrane forms a protecting 
sheath for the cranial or spinal nerves piercing it. 

THE DURA MATER. 2 

Structure and Relations. — It is a very dense and inelastic 
membrane composed of white fibrous and yellow elastic tissue. 
It is lined with flat endothelial cells which constitute its 
internal surface. The dura is made up of two layers, but 
they are in most places closely united. The external layer 
constitutes, the endosteum of the cranial bones. It is their 
nutrient membrane. Through the cranial foramina and 
sutures it is continuous with the external periosteum. The 
internal layer of the dura separates from the outer layer, at 
the foramina, to form sheathes for the nerves and, along 
the sinuses, to form the internal boundary of those venous 
spaces and to produce the great incomplete partitions, called 
processes, which project centrally into the great fissures of 
the brain. 

Processes. — From the inner surface of the dura the groat 
processes 3 are given off. The falx cerebi and falx cerebelli 
hang vertically in the great longitudinal fissure of the cere- 

(1) Meninges encephall. (3) Processus dura matris. 

(2) Dura mater encephali. 



2 THE BRAIN AND SPINAL CORD. 

brum and the posterior notch of the cerebellum; and, into 
the great transverse fissure, extends horizontally the ten- 
torium-cerebelli. The falx cerebri is attached in front to 
the crista galli and behind to the internal occipital protuber- 
ance and superior surface of the tentorium; the falx cere- 
belli continues from the inferior surface of the tentorium, 
along the occipital crest, to the posterior border of the fora- 
men magnum. The attachment of the tentorium cerebelli 
is to the internal protuberance and the lateral arms of the 
crucial ridge forward to the petrous bone; and, then, it is 
along the superior border of the petrous bone to the clinoid 
processes of the sphenoid. A large median notch between 
its anterior border and the dorsum ephipii, incisura tentorii, 
transmits the mid-brain. The diaphragm sellse is a small 
centrally perforated sheet of dura which covers the pituitary 
fossa. 

Sinuses. — Large venous passages lined with endothelial 
cells, and called sinuses, are situated between the layers of 
the dura. In the convex and in the free border of the falx 
cerebri are, respectively, the superior 4 and the inferior 4 lon- 
gitudinal sinus. The superior extends from the foramen 
caecum back to the torcular Herophili, 5 at the internal 
occipital protuberance. Joining the common vein 6 of Galen, 
at the margin of the tentorium, the inferior longitudinal 
sinus becomes the straight, 7 whose course is through the 
middle of the tentorium to the torcular. The occipital sinus 8 
(or sinuses) traverses the falx cerebelli from the foramen 
magnum upward to the same point. In the torcular Hero- 
phili the lateral sinuses 9 rise. Grooving the horizontal arms 

(4) Sinus sagitalis superior, et inferior. 

(5) Confluens sinuum. 

(6) Vena cerebri magna. 

(7) Sinus rectus. 

(8) Sinus occipitalis. 

(9) Sinus traversus (sing.). 



THE MENINGES OF THE BRAIN. 3 

of the crucial ridge, each runs outward in the tentorium to 
the base of the petrous bone, where it receives the superior 
petrosal sinus; 10 it then turns downward through the sig- 
moid fossa and unites with the inferior petrosal sinus in the 
jugular foramen. Situated on either side of the sella Tur- 
cica is a continuation of the ophthalmic vein, the large 
cavernous sinus, 11 whose division at the apex of the petrous 
bone forms the two petrosal sinuses. 10 The circular sinus 12 
(around the sella) joins the two cavernous to each other; 
and the inferior petrosal sinuses communicate with one 
another through the transverse or basilar sinus. 13 The 
petrosal sinuses, from the bifurcation of the cavernous sinus, 
follow outward the coresponding border of the petrous bone; 
the superior petrosal empties into the lateral sinus at the 
base of the petrous bone; and the inferior petrosal, running 
outward to the jugular foramen, unites with the lateral sinus 
in forming the internal jugular vein. 

Along and within the superior longitudinal sinus are the 
Pacchionian bodies, 14 They are enlarged villi of the arach- 
noid, and seem to afford an outlet for the sub-arachnoid 
fluid into the superior longitudinal sinus. 

The arteries which supply the dura are the anterior ami 
posterior ethmoidal from ophthalmic; from internal carotid, 
the anterior meningeal; the great and small meningeal 
which are branches of internal maxillary ; meningeal 
branches of the ascending pharyngeal and occipital; ami 
the posterior meningeal from the vertebral artery. 

The middle meningeal 1 * is largest. It is accompanied 

(10) Sinus petrosus superior, et inferior. 

(11) S. cavernosus. 

(12) S. circularis. 

(13) S. basilaris. 

(14) Granulationes arachnoideales. 
• (ir>) Arteria meninges media 



4 THE BRAIN AND SPINAL CORD. 

by a vein and surgically is important because of its course 
over the motor area. Ascending' from the foramen spinosum 
it divides near the upper border of the squamosa into two 
large branches, the anterior and posterior. The posterior 
runs horizontally backward just below the squamo-parietal 
suture and then ascends over the posterior half of the parietal 
bone. The anterior branch runs upward a half -inch behind 
the coronal suture. It may be located, according to Quain, 
at one inch, one inch and a half, and two inches behind 
external angular process and above the zygoma. 

The following nerves give branches to the dura : — troch- 
lear, ophthalmic, Gasserian ganglion, the tenth and twelfth 
cranial; and the sympathetic. , The motor fibers supply the 
meningeal arteries. 

Six points of difference in the dura of the cord. — Absence 
of processes, of sinuses, of Pacchionian bodies, and of perios- 
teal function. It is covered on both surfaces by endothelium 
and separated from the vertebrae by areolar tissue, fat and 
the meningo-rachidian veins. 

ARACHNOID OR BRAIN. 

In structure it is a delicate, fibrous, web-like membrane 
covered externally with endothelium. Internally it is joined 
to the pia mater by innumerable fibrous trabecule, the sub- 
arachnoid tissue. The trabecular and all spaces formed by 
them possess a single layer of endothelial cells. Conical 
elevations of fibrous tissue with their investing epithelium 
constitute the villi seen on the outer surface. 

Relations. — The arachnoid 16 follows the inner surface of 
the dura and is prolonged, as a sheath, upon the nerves which 
pierce it. It does not dip into the sulci of the brain. From 

(16) Arachnoidea encephali. 



THE MENINGES OF THE BRAIN. 5 

the pia it is separated by the subarachnoid spaces. 17 The 
anterior subarachnoid space (cisterna pontis, interpedularis 
et chiasmatis), in front of the medulla, pons and mid-brain 
and between the temporal lobes of the cerebrum; and the 
posterior (cisterna cerebello-medullaris) between the med- 
ulla and cerebellum, contain most of the subarachnoid fluid. 
The posterior communicates with the fourth ventricle 
through the foramen of Magendie 18 and the foramina of 
Key and Eetzius. 19 

The vessels seen for a short distance in the arachnoid 
belong to the pia mater. Its nerves are doubtful. Perhaps 
branches of the inferior maxillary, of the facial and of the 
spinal accessory supply it. 

In the arachnoid of the cord fewer trabecular join it to 
the pia; and these, in great part, are collected to form a 
fenestrated septum in the posterior median line. The 
medulla spinal veins are covered by the arachnoid, lying 
between it and the pia. 

PIA MATER OF THE BRAIN. 20 

Structure. — It is a vascular membrane composed of a close 
network of veins and arteries held together by fibro-elastic 
areolar tissue. The endothelium covering its outer surface 
is continuous with that of the subarachnoid trabecular and 
spaces. Eelations. — The pia closely follows the brain sur- 
face. Internally, it sends supporting trabecular into the 
brain, which transmit blood-vessels; and externally il forms 
an investing sheath for the cranial nerves. Two important 
processes are formed by it; the velum interpositiiro (help- 
ing to form the anterior choroid tela- 1 ) is bucked into the 

(17) Cavum subaraehuoideale (sing.). 

(18) Apertura mediana ventriculi quarti. 

(19) Apertura lateralis ventriculi quarti (suilv.). 

(20) Pia mater encephali. 

(21) Tela choroidea ventriculi tertii. 



6 THE BRAIN AND SPINAL CORD. 

choroid (anterior great transverse) fissure between the fornix 
and the inter-brain. A second process is tucked in over the 
fourth ventricle, between the medulla and cerebellum. It 
helps to form the posterior choroid tela, 22 which roofs over 
the posterior part of the fourth ventricle, and is of triangular 
shape. The posterior choroid tela is pierced by three fora- 
mina (Magendie, and Key and Betzius). They open into 
the fourth ventricle. 

The arteries of the pia are the anterior, middle and pos- 
terior cerebral, the anterior and posterior choroids, and the 
anterior and posterior inferior cerebellar and superior cere- 
bellar with many branches. 

Veins are numerous in the pia; the veins of Galen and 
of the choroid plexuses of the lateral, third and fourth 
ventricles; cerebral veins, superior, medial and inferior; 
and ' superior, lateral and inferior cerebellar veins. All of 
them empty into the sinuses. 

Seven cranial nerves — 3rd, 5th, 6th, and 7th, 9th, 10th 
and 11th, and the sympathetic supply the pia mater and 
its blood-vessels. 

The pia mater of the spinal cord has two layers, the 
outer of which is the more vascular and contains the spinal 
arteries and the tributaries of the medulli-spinal veins. It 
forms three processes, namely, the anterior septum, which 
occupies the anterior median fissure, and the ligamenrum 
dentieulatum of each side. 

TABLE 1. 

GRAND DIVISIONS OF BRAIN. 

The brain may be conveniently studied in four grand 
divisions : 

(22) Tela choroidea ventriculi quarti. 



THE MENINGES OF THE BRAIN. ; 

I. Cerebrum, 23 composed of — 

1. Hemispheres, 24 which include: 

Their cortex and medulla, 
Corpora striata, and 
Olfactory lobes, 

With connecting links of the hemispheres: 

Corpus callosum, 

Fornix, 

Commissura hippocampi and 

Anterior commissure and 

2. Inter-brain, 25 or Thalamencephalon, which in- 

cludes : 
Lamina cinerea, 

Tuber cinereum and infundibulum, 
Corpora albicantia, 
Optic thalami, 

Middle commissure, and posterior (in part), 
Pineal body, 

External geniculate bodies, 
Optic tracts and commissure. 
II. Mid-brain, Crus Cerebri, or Pedun cuius Cerebri 26 
Crustse, (the bases or pedes pedunculi) 
Substantia nigra 
Tegmentum 
Corpora quadrigemina 
Internal geniculate bodies. 
III. Hind-brain 27 — 
Pons 

Cerebellum 
IV. After-brain 28 — 
Medulla. 



(23) Prosencephalon. (26) Mesencephalon. 

(2i) Telencephalon. (27) Metencephalon. 

(25) Dlencephalon (28) Myelencephalon. 



CHAPTER II. 



THE CEREBRUM. 

The cerebrum is that part of the brain which especially 
characterizes man. In man only does it reach such pre- 
dominant development. Though a mere outgrowth of the 
anterior brain-vesicle in the beginning, it completely over- 
shadows all other parts of the brain by the seventh month 
of embryonic life, extending farther forward, backward and 
lateralward than any other part. Reference to the table 
given above, shows that the cerebrum is made up of the 
hemispheres and the inter-brain. It constitutes an ovoid 
mass, flattened interiorly, which fills the vault of the cranium 
and rests, below, upon the floor of the cranial cavity in the 
anterior and middle fossae and upon the tentorium cerebelli 
over the posterior fossa. Viewed from above, it is suffi- 
ciently round to suggest a sphere; and, being divided in 
the median line by the great longitudinal fissure, the lateral 
halves are called hemispheres. In the floor of the great 
longitudinal fissure the corpus callosum can be seen joining 
the hemispheres together; and beneath it, concealed from 
view, are the fornix, anterior commissure, and commisura 
hippocampi. Those are the connecting links, proper, of the 
hemispheres. Inferior to them, is found the inter-brain. 
The latter forms an additional union of the hemispheres, as 
may be seen by viewing the base of the brain. In order to 
fix important landmarks and to learn the location and rela- 



THE CEREBRUM. 9 

tions of the gross structures of the cerebrum, it is necessary 
to study in detail the topography of the exterior and interior 
surface. It is that with which the present chapter deals. 
For the minute anatomy of the cerebral structures, see 
Chapter IV. 

Section 1. The Exterior Surface. 

The exterior surface 2 of the cerebrum 1 is composed of a 
thin sheet of gray matter varying in thickness from one- 
sixth to one-quarter of an inch. That gray matter forms a 
bark-like covering for the underlying white substance and 
is, therefore, called the Cortex. It is thrown into irregular 
elongated folds named Convolutions, or Gyri, by deep linear 
depressions, which greatly increase the relative amount of 
cortical substance. The linear depressions are called Fis- 
sures, or Sulci; and, in consequence of them, the gray 
substance is increased in bulk to 58-J- per cent of the entire 
cerebrum (De Eegibus). 

The exterior surface is conveniently studied in three re- 
gions, namely; the Convex Surface, the Medial and Tento- 
rial Surface, and the Basal Surface. 

fissures op tpie convex surface. 

Two fissures are very extensive. The great longitudinal 
fissure 3 separates the hemispheres of the cerebrum. It con- 
tains the falx cerebri. The cerebrum is separated from the 
cerebellum by the great transverse fissure. 4 This fissure 
continues forward above the mid-brain, and terminates in 
the cerebrum between the inter-brain and the hemispheres 
as choroid fissure. The tentorium occupies its posterior 
part. The fissnra choroidea contains the velum interposi* 

(1) Prosencephalon. 

(2) Facies convexa. 

(3) Fissnra longitudinalis cerebri. 

(4) Fissnra transversa cerebri. 



10 THE BRAIN AND SPINAL CORD. 

turn. Three interlobular fissures 5 are found on the convex 
surface of each hemisphere : 

(1) The Fissure of Sylvius 6 begins in the vallecula at the 
base of the brain. It runs outward between the frontal and 
the temporal lobe, along the lesser wing of the sphenoid 
bone; and, turning upward, on the convex surface it divides 
into an anterior, a vertical and a horizontal ramus. Into 
the frontal lobe project the small anterior and vertical rami 
They are separated by the foot (posterior end) of the infe- 
rior frontal gyrus, called the frontal operculum (operculum, 
a cover). Below the anterior ramus is a knuckle of the 
same frontal convolution which forms the orbital operculum : 
and, between the vertical and horizontal rami, is located the 
fronto-parietal operculum, constituting the connecting gyrus 
between the precentral and postcentral convolutions. The 
opercula cover the Island of Eeil. The horizontal limb of 
the Sylvian fissure separates the temporal lobe from the 
parietal. Near the crotch and within the fissure of Sylvius 
is -situated the island of Reil. A line drawn from a point 
one and one-quarter inches behind the external angular 
process of the frontal and one and a half inches above the 
zygoma, backward to a point three-quarters of an inch below 
the parietal eminence, lies directly over the horizontal ramus 
of this fissure. 

(2) Fissure of Rolando. — Beginning just above the hori- 
zontal limb of the fissure of Sylvius, is the fissure of Rolando, 
or Central fissure, 7 which extends upward and backward 
almost to the great longitudinal fissure. Its upper extrem- 
ity is about half an inch behind the middle of a line drawn 
from the nasal eminence to the external occipital protuberr 

(5) Fissuras interlobulares. (7) Sulcus centralis. 

(6) Fissura lateralis cerebri. 



THE CEREBRUM. II 

ance (the sagittal meridian). With this line the fissure of 
Eolando forms an anterior angle of 67 degrees. The fissure 
of Eolando forms the boundary between the frontal and the 
parietal lobe. It is developed in two parts., superior and 
inferior, which join at an angle open backward, the genu, 
and both parts may present an anterior concavity. 

(3) Parieto-occipital Fissure. 8 — If the line locating the 
horizontal limb of the fissure of Sylvius be extended back to 
the sagittal meridian its posterior end marks the location of 
the parieto-occipital fissure (external part). The greater 
part of this fissure is on the internal or medial surface of 
the hemisphere. To the extent of half an inch the external 
parieto-occipital fissure separates the parietal and occipital 
lobes from each other. 

LOBES AND CONVOLUTIONS OF THE CONVEX SURFACE. 

( I ) The Frontal Lobe 9 comprises the anterior polar region 
of the hemisphere back to the Rolandic and the Sylvian 
fissure. It is subdivided by three sulci : the precentral 
sulcus 10 (superior and inferior parts), which is parallel with 
the fissure of Rolando (central), and the superior and infe- 
rior frontal sulci. 11 The two latter extend downward and 
forward from superior and inferior precentral sulci, respec- 
tively, and separate from each other the superior, middle ami 
inferior frontal convolutions. 12 The ascending frontal eon- 
volution 5 (precentral) lies between the precentral sulcus and 
the fissure of Rolando. It is joined (o the ascending parietal 
convolution 13 (postcentral) by the paracentral lobule, 14 

(8) Sulcus occipito-parietalis. 

(9) Lobus frontalis. 

(10) Sulcus praecentralis. 

(II) S. frontalis superior, inferior. 

(12) Gyrus frontalis superior, medius, Inferior. 

(13) G. centralis anterior, posterior. 

(14) Lobulus paracentralis. 



12 THE BRAIN AND SPINAL CORD. 

above the central fissure, and by the fronto-parietal opercu- 
lum, below it. The fronto-parietal operculum and posterior 
part of the inferior frontal gyrus constitute the region of 
speech. In the foot (posterior end) of th? middle frontal 
gyrus is the writing center (Gordinier). 

(2) The Parietal Lobe 15 is situated behind the fissure of 
Kolando and above the horizontal limb of the Sylvian fissure. 
From the posterior end of the latter to the external parieto- 
occipital fissure, the lobe is separated from the temporal, 
below, and the occipital, behind, by an imaginary line. The 
sulci of this lobe are the intraparietal, 16 with an anterior 
and a posterior ramus (joined by the genu) which are par- 
allel with the central and the great longitudinal fissures, 
respectively; and the post-central sulcus, 17 which ascends 
from the genu of the intraparietal almost to the great longi- 
tudinal fissure. The anterior limb of the intraparietal fis- 
sure and the post-central sulcus separate the ascending 
parietal convolution 18 from the superior parietal and inferior 
parietal. 19 The posterior limb of the intraparietal fissure 
separates the superior and inferior parietal convolutions from 
each other. Indefinite sulci subdivide the inferior parietal 
into supra-marginal, 20 angular, 21 and postparietal gyri, which 
wind over the upturned ends of the Sylvian and first and 
second temporal sulci, respectively. The best known motor 
areas of the cortex are contained in the ascending frontal, 
ascending parietal and superior parietal gyri, in the foot of 
the inferior and middle frontal convolutions; in the quad- 
rate and paracentral lobules, and in the marginal gyrus 

(15) ILobus parietalis. 

(16) Sulcus interparietalis. 

(17) S. postcentralis. 

(18) Gyrus centralis posterior. 

(19) Lobulus parietalis superior, inferior. 

(20) Gyrus supramarginalis. s 

(21) Gyrus angularis. 



THE CEREBRUM. 13 

The area of general sensation, somaesthetic area, 22 nearly 
coincides with the great motor areas; it is a little more 
extensive. 

(3) Occipital Lobe. 23 — It forms the posterior pole of the 
hemisphere. With the parietal and temporal lobes it is 
directly continuous, being marked off from them by an 
imaginary line drawn from the pre-occipital notch to the 
external parieto-occipital fissure. The parieto-occipital fis- 
sure bounds it to the extent of half an inch. Its sulci 24 and 
convolutions vary much; usually the following are found: 
the superior occipital sulcus, vertical, or logitudinal, in di- 
rection, and the middle 24 and inferior, which are horizontal, 
divide the lobe into superior, middle and inferior convolu- 
tions. 25 The superior occipital sulcus is often continuous 
with the intraparietal fissure. The inferior occipital sulcus 
follows the lower border of the convex surface. The supe- 
rior and inferior convolutions form the coresponding borders 
of the lobe and trend toward the occipital pole. The middle 
occipital gyrus is in the angle between them and may reach 
the medial border. The visual memory center is located in 
the convex surface of the occipital lobe and in the angular 
gyrus. 

(4) The Temporal Lobe 26 is that part of the cerebral hemi- 
sphere behind the main stem and below the horizontal limb 
of the fissure of Sylvius. It rests in the middle fossa of the 
skull; and is probably the seat of the centers of taste, of 
smell and of hearing. The first temporal sulcus 2 (or par- 
allel sulcus) and the second temporal sulcus- 7 divide the 

(22) Soma— body — Aesthesis— perception, or feeling. 

(23) Lobus occipitalis. 

(24) Sulci occipitales laterales. S. oc. transversus. 

(25) Gyri occipitales laterales. 

(26) Lobus temporalis. 

(27) Sulcus temporalis superior, medius. 



14 THE BRAIN AND SPINAL CORD. 

lobe into three horizontal convolutions, named, from the 
Sylvian fissure downward, the first, second and third tem- 
poral convolutions. 28 In the third and fourth fifths of the 
first temporal convolution, and in the transverse temporal 
gyri, concealed in the fissure of Sylvius, is the center of 
hearing (Barker). 

Annectant convolutions are small links joining the greater 
gyri. The first annectant joins the superior parietal and supe- 
rior occipital convolutions. To the middle occipital gyrus, 
the angular or postparietal is linked by the second annectant 
and the middle temporal by the third. The fourth annectant 
unites the inferior temporal and inferior occipital convolu- 
tions. There are other less constant annectants. 

(5) The Island of Reil 29 is also called the central lobe. 
Situated within the fissure of Sylvius, it is bounded at the 
base of the brain by the sulcus limitans insulse (anterior, 
external and posterior). 30 The sulcus centralis insulae di- 
vides it into anterior and posterior lobule, each of which is 
composed of from two to four convolutions. 31 The fronto- 
parietal operculum and inferior frontal convolution 'cover 
the insular convolutions, hence the name, gyri operti, also 
applied to them. 

FISSURES OF THE MEDIAL AND TENTORIAL SURFACE. 

The middle third of this surface 32 is made by sagittal 
section through the connecting links of the hemispheres and 
the inter-brain. The free surface presents six fissures. 

(1) Calloso-marginal Fissure. — Beginning under this 
middle cut surface and extending forward, upward and back- 

(28) Gyrus temporalis superior, medius, inferior. 

(29) Insula. 

(30) Sulcus circularis (Reili). 

(31) Gyri insula?— G. breves, Gyrus longus. 

(32) Facies medialis. 



THE CEREBRUM. 1 5 

ward until it half encircles the corpus callosum; and then 
turning upward to the convex border and ending just behind 
the fissure of Rolando, is the calloso-marginal fissure. 38 It 
separates the gyrus fornicatus and the marginal convolution 
from one another by its anterior part ; and, by its upturned 
posterior end, separates the paracentral lobule from the 
quadrate lobe. 

(2) The Parieto-occipital Fissure (internal part) 34 ex- 
tends upward and backward from just beneath the thick 
posterior margin of the corpus callosum, the splenium, to 
the border of the medial surface, where is it continuous with 
the external parieto-occipital fissure. It is situated between 
the quadrate and the cuneate lobe. 

(3) Calcarine. — From near the middle of the parieto- 
occipital, the calcarine fissure 35 extends in a curve downward 
and backward between the cuneate lobe and the fifth temporal 
(lingual) convolution and ends bifid. The anterior part of 
the parieto-occipital fissure, in its formation, may be com- 
mon either to that fissure or to the calcarine. 

(4) Hippocampal Fissure. — -A crescentic fissure, convex 
downward, winds from the splenium of the corpus callosum 
forward beneath the optic thalamus nearly to the end of 
the temporal lobe, where it is closed by the uncus. It 
is the dentate or hippocampal fissure. 30 On the surface of 
the temporal lobe this fissure appears to be identical with the 
temporal extension of the great transverse fissure (or choroid 
fissure) ; but, deeply, it lies posterior to it and is separated 
from the choroid fissure by the fascia dentata. 

(5) Choroid Fissure. — It is of horseshoe shape ami ex- 
tends from the foramen of Monro backward, — and down- 
ward, — and forward to near the pole of the temporal lobe. 

(33) Sulcus cinguli. , (36) P. hippocampi. 

(34) S. parieto-occipi talis. (37) Fissura choroidea, 

(35) Fissura calcarina. 



l6 THE BRAIN AND SPINAL CORD. 

On its convexity it is bounded by the fornix. The fissure is 
a complete one, involving the whole hemisphere wall. A 
single layer of epithelium separates it from the lateral ven- 
tricle. The pia mater, dipping into it, forms the choroid 
plexus of that ventricle. The fissure is again peculiar in 
the fact that between the roof of the third ventricle and the 
fornix it is directly continuous with the same fissure on the 
opposite side. In this antero-superior part, which is in direct 
continuity with the great transverse fissure, is the velum 
interpositum. 

(6) The Long Collateral Fissure 88 is situated below the 
dentate, parietooccipital and calcarine fissures. The collat- 
eral fissure bounds, inferiorly, the hippoeampal and the fifth 
temporal convolution; and separates them from the fourth 
temporal (or fusiform) gyrus. 

LOBES AND CONVOLUTIONS OF MEDIAL AND TENTORIAL SUR- 
FACE. 

They form two concentric rings, interrupted antero-infe- 
riorly at the vallecula Sylvii, which encircle the corpus 
callosum and optic thalamus. The two rings are separated 
from one another by a broken fissure, the limbic fissure, made 
up by the calloso-marginal (except its posterior end), the 
post-limbic sulcus, and the anterior part of the parieto- 
occipital and collateral fissures. 

Central Ring*. — The gyrus fornicatus 39 and hippoeampal 
convolution 40 joined by the isthmus, 41 at the posterior border 
of the corpus callosum, form the central ring. The former 
begins under the corpus callosum in the frontal lobe anterior 
to the fissure of Sylvius ; and the latter terminates as uncus 
just behind that fissure in the temporal lobe. The central 
ring forms the chief part of the limbic lobe. 

(38) Fissura collaterals. (40) Gyrus hippocampi. 

(39) Gyrus cingnli. (41) Isthmus gyri fornicati. 



THE CEREBRUM. \J 

The Peripheral Ring, from before backward, is composed 
of the marginal convolution/ 2 ending in the paracentral 
lobule 43 ; the quadrate lobe/ 4 bounded antero-inferiorly by 
the post-limbic sulcus ; the cuneate lobe 45 ; the fifth tempo- 
ral convolution (infracalcarine, or lingual) 46 ; and the fourth 
temporal, or fusiform, convolution. 47 A slight sulcus (third 
temporal) separates the last from the third temporal gyrus 
on the convex surface. The quadrate and paracentral lob- 
ules and the posterior third or half of the marginal gyrus 
contain motor centers, for the opposite side of the body, the 
bead, arm, trunk and leg centers being located in this order 
from before backward. 

The uncinate convolution is the combined hippocampal 
and fifth temporal gyri. 

Limbic Lobe. — It is composed of the following parts, viz. : 
(1) the gyrus fornicatus and hippocampal convolution; (2) 
the nerves of Lancisi and peduncle of the corpus callosum; 
and (3) the pillars and half the body of the fornix, one-half 
of the septum lucidum, and the fascia dentata. It is en- 
circled by the limbic fissure. The limbic lobe probably con- 
tains the centers of smell and taste which are localized in the 
hippocampal gyrus and uncus. Together with the olfactory 
lobe it constitutes the Ehinencephalon. 

BASAL OR INFERIOR SURFACE. 

The basal surface of the cerebrum 48 comprises the inferior 
surface of the hemispheres and of the inter-brain. It ex- 
tends from the anterior poles of the hemispheres hark to (he 
fissure of Sylvius, laterally; and, in the median line, to the 

(42) Gyrus frontalis superior. (46) Gyrus ling;imlis. 

(43) robulus parnoontrnlis. (17) Cyrus fusiformis. 

(•14) Precuneus. (48) Fades basalls cerebri 

(45) Cuneus. 



18 THE BRAIN AND SPINAL CORD. 

posterior perforated lamina and crustse of the mid-brain. 
The great longitudinal fissure splits it into lateral halves in 
front, separating the frontal lobes of the cerebrum from 
each other. The fissure extends back to the upturned part 
^lamina terminalis) of the lamina cinerea and to the corpus 
callosum. The length of the fissure is considerably less than 
one-third of the cerebral axis. 

The medial structures of this surface, named from before 
backward^ are as follows: 

Lamina cinerea, 

Optic chiasm, or optic commissure, 

Tuber cinereum and infundibulum, 

Pituitary body, 

Corpora albicantia. 
These are often called interpeduncular stuctures. Con- 
stituting the base of the inter-brain, they form a continuous 
sheet beneath the third ventricle and optic thalami, which 
joins, antero-laterally, the anterior perforated lamina and the 
cortex of the internal orbital convolution. 

The lamina cinerea is the most anterior of the medial 
structures. It is a thin lamina of ash-colored- (cinereum) 
gray matter. Arching from behind forward over the supe- 
rior surface of the optic commissure to which it is attached, 
it then turns upward and backward, the reflected part con- 
stituting the lamina terminalis, and meets the rostrum of 
the corpus callosum- In the angle of turning is the optic 
recess. The lamina terminalis, which is seen in ihe floor of 
the great longitudinal fissure, forms part of the anterior 
boundary of the third ventricle. 

Tuber Cinereum. — At the posterior border of the optic 
commissure, the lamina is continuous with the tuber cine- 
reum. Here the gray matter is thickened and centrally 



THE CEREBRUM. I9 

prominent. The bulbous infundibulum projects downward 
from it to rest in the sella Turcica, where it forms the pos- 
terior lobe of the pituitary body. The upper half of the 
infundibulum is hollow (funnel-like). Its cavity forms the 
lowest part of the third ventricle. In man the bulb of 
the infundibulum is solid at maturity, though hollow in 
the embryo. It is composed largely of fibrous tissue notwith- 
standing the fact that it is developed from the floor of the 
Thalmencephalon. From the base (superior end) of the in- 
fundibulum, the tuber cinereum extends in continuity with 
the anterior perforated lamina and hypothalamic gray matter 
on each side of it; and, behind, the corpora albicantia mark 
the boundary between it and the posterior perforated lamina 
of the mid-brain. 

The lamina cinerea and tuber cinereum form the inferior, 
or great, gray commissure of the inter-brain. 

The pituitary body (hypophysis) is composed of two lobes 
bound together by connective tissue. A sheet of dura mater 
(diaphragma sellse) holds them in the pituitary fossa. The 
anterior lobe, the larger, is derived from the epithelium of 
the mouth cavity; and, in structure, resembles the thyroid 
gland. Its closed vesicles, lined with columnar epithelium 
(in part ciliated), contain a viscid jelly-like material (pitu- 
ita), which suggested the name for the body. The anterior 
lobe is hollowed out on its posterior surface and receives the 
posterior lobe, the infundibulum, into the con-cavity. The 
pituitary body appears to have an inhibitive action on growth 
and is found diseased in acromegalia. 

Corpora Albicantia. — Two white bodies, as Large as a small 
pea, the corpora albicantia, 49 arc situated one on cither side 
of the median line, between the tuber cinereum and the pig- 

(4!)) Corpora mamillaria. 



20 THE BRAIN AND SPINAL CORD. 

mented gray matter of the posterior perforated lamina. Each 
is formed by a loop in the anterior pillar of the fornix and 
is, therefore, composed of white fibers on the surface. There 
is gray matter in the interior, which may contain the ends of 
the fornix fibers and be the seat of origin of the ascending 
bundle, the bundle of Vicq d'Azyr. 50 The latter terminates 
in the optic thalamus. 

Immediately behind the corpora albicantia is the posterior 
perforated lamina. This is the exposed part of the substan- 
tia nigra of the mid-brain, perforated for the passage of the 
postero-median ganglionic arteries to the optic thalami and 
walls of the third ventricle. The pons and crustae bound it 
behind. Issuing from the inner side of the crusta 51 is the 
large motor oculi, or third cranial, nerve 52 ; and coursing 
over its surface from behind forward, is the smaller fourth 
nerve. 53 The crustae will be described with the mid-brain to 
which they belong. 

The Optic Chiasm (chiasma opticum) remains to be de- 
scribed. It is situated medially beneath the lamina cinerea, 
in the optic groove of the sphenoid bone. The fibers of the 
optic nerves and tracts compose it. There are three sets of. 
these fibers, namely, the inter-cerebral, direct and decussat- 
ing. A fourth group of fibers, called inter-retinal and said 
to be commissural for the retinae, has been hitherto described, 
but their existence is very doubtful. The intercerebral fibers 
are not found in the optic nerves, but form a commissure 
(Gudden's) for the internal geniculate bodies. The direct 
and decussating fibers run through tract and nerve and join 
the brain with the retina of the same and of the opposite 

(50) Fasciculus thalamomamillaris. 

(51) Basis pedunculi cerebri (sing.). 

(52) Nervus oculomotorius. 

(53) N. trochlearis. 



THE CEREBRUM. 21 

side, respectively. In most vertebrates below mammals and 
in the mouse and guinea pig, the optic fibers all decussate 
in the chiasm. Normally in man and the higher mammals, 
the lateral half of each retina receives direct fibers and the 
medial half crossed fibers. The optic nerves 54 extend from 
the front of the commissure into the orbits through the optic 
foramina and terminate in the ganglionar cells of the retinae. 
The optic tracts 55 connect the commissure with the brain. 
Each tract winds outward and backward around the cerebral 
peduncle, and divides into an internal and an external root. 50 
The roots wind around the optic thalamus and disappear 
(superficial origin) at the corresponding geniculate body. The 
fibers of the external root may be traced to the external genic- 
ulate body (80 per cent Von Monokow), to the optic thala- 
mus (nearly all the 20 per cent remaining), and the rest to 
the anterior quadrigeminal body. The optic radiations of 
the internal capsule connect these centers with the medial 
occipital cortex. The internal root rises from the internal 
geniculate body and optic thalamus. The nuclei of the optic 
libers are probably connected with the cerebellum by the 
fillet. 

Notice now the lateral part of the base of the cerebrum, 
which is the base of the hemispheres. 

Orbital Lobe. — The inferior surface of the frontal lobe, 
resting on the orbital plate of the frontal bone, is called the 
orbital lobe. 57 It is separated from its fellow by the great 
longitudinal fissure, and is bounded behind by the vallecula 
Sylvii and fissure of Sylvius, overlapped by the temporal 
lobe. More accurately, the posterior boundary is the ante- 
rior perforated space and the anterior fissure of Eeil. The 
orbital lobe is concave transversely and is divided by a tri- 

(54) Nervi optici. (56) Radix medialis, lateralis. 

(55) Tractus optici. (57) Lobus orbi talis. 



22 THE BRAIN AND SPINAL CORD. 

radiate, or an H-shaped fissure, 58 directed fore and aft, into 
internal, anterior and posterior orbital convolutions. 59 The 
internal orbital convolution lies beside the great longitudinal 
fissure, and is continuous with the marginal convolution on 
the medial surface. Its anterior end joins the superior 
frontal convolution; its posterior, the trigone and area of 
Br oca. The internal orbital convolution is subdivided by 
the sulcus olfactorius, which contains the olfactory tract; 
and that part of the convolution medial to the olfactory fissure 
is called the gyrus rectus. The anterior and posterior or- 
bital convolutions may be traced to the convex cerebral 
surface in continuity with the middle and inferior frontal 

If the anterior part of the temporal lobe be removed, the 
under surface of the island of Eeil. is brought into view. 
The sulcus limitans insulag 60 bounds it on three sides (ante- 
rior, external and posterior), and separates it from the pos- 
terior orbital gyrus, in front; the frontal and fronto-parietal 
opercula, externally; and from the temporal lobe, behind. 
(See lobes of convex surface.) 

Olfactory Lobe. — This term includes the remainder of the 
structures forming the inferior surface of the cerebrum. The 
reason for calling them the olfactory lobe 61 is found in the 
lower animals; and in the human embryo, where it exists 
as a prominent hollow process of the cerebral hemisphere. 
A constriction (fissura prima) divides this diverticulum into 
the anterior and posterior olfactory lobule. In the human 
adult the anterior olfactory lobule is represented by the bulb, 
the tract, the trigone and the area of Broca. The anterior 
perforated lamina (or space) represents the posterior lobule. 

The Olfactory Bulb 62 is an ovoid mass of brain matter 



(58) 


Fissurse orbitales. 


(61) Lobus olfactorius. 


(59) 


Gyri orbitales. 


(62) Bulbus olfactorius. 


(60) 


Sulcus circularis (Reili). 


i 



THE CEREBRUM. 23 

about a half-inch long and one-sixth of an inch in diameter. 
It rests between the orbital lobe and the cribriform plate of 
the ethmoid bone. Below and on each side, it is composed 
of cortical gray matter (four layers) from which rise the 
twenty or thirty olfactory nerves. 63 The nerves, after enter- 
ing the nasal fossa through the cribriform plate, are distrib- 
uted to the Schneiderian membrane. The cells of Max 
Schultze in the Schneiderian membrane are the real cell- 
bodies of the olfactory nerve fibers (axones), hence the latter 
grow upward to the bulb. The fibers form the first layer of 
the bulb, olfactory nerve layer, and arborize about the 
dendrites of the large mitral cells to form the second layer,— 
the stratum glomerulosum. In the third layer of the gray 
matter are found great mitral cell-bodies, whose medullated 
axis-cylinders, or axones, form the white matter of the bulb : 
and, continued backward, constitute the olfactory tract. 

Olfactory Tract. — The tract 64 is triangular in section, 
nearly an inch long and one line in width. It is concealed 
in the olfactory sulcus. At its base it divides into external 
and internal root, 65 which inclose between them the trigone 
into which some fibers may be traced, forming the middle 
root. 65 The external root courses backward and outward and 
terminates in the uncus at the anterior extremity of the 
hippocampal convolution. It crosses the anterior perforated 
space. The internal root bends sharply inward, toward the 
median line, and runs between the trigone and area of "Rroea. 
Its fibers turn into Broea's area and the gyrus fornicatus. 
Thus the two roots unite the opposite ends of the limbic lobe 
From the bifurcation of the olfactory tract, a few fiber- 
proceed into the trigone and frontal lobe. 

(63) Nervi olfactorii. 

(64) Tractus olfactorius. 

(65) Striae olfactoriae, lateralis, medialis, intermedia. 



24 THE BRAIN AND SPINAL CORD. 

The Trigone and Area of Broca. — The triangular portion 
of cortex between the inner and outer olfactory roots, called 
the trigone, 66 is continuous medially with Broca's area. 67 
The internal root marks the boundary between them. Both 
are bounded behind by the fissura prima (transverse part), 
and the oblique part of the same fissure separates the area 
of Broca from the peduncle of the corpus callosum. The 
area of Broca is limited in front by a slight curved depres- 
sion, the fissura serotina. On the medial surface, Broca's 
area joins the gyrus fornicatus. 

Some of the fibers of the middle root of the olfactory tract 
probably pass through the anterior commissure; and, after 
piercing the opposite corpus striatum, terminate in the tem- 
poral lobe. They constitute the only olfactory decussation 
known. 

The posterior olfactory looule is identical with the anterior 
perforated lamina. 68 It is separated from the trigone by the 
transverse fissura prima. Internally, it is in direct continu- 
ity with the lamina cinerea. The optic tract bounds it, 
postero-medially. Externally, it forms the floor of the valle-. 
cula Sylvii, where it is overlapped by the temporal lobe. 
Superiorly, it is continuous with the base of the corpus 
striatum. Coursing over the inner and outer border of the 
anterior perforated lamina, are the collosal peduncle and 
external olfactory root, which converge and meet in the 
hippocampal convolution. The perforations of the lamina 
are for the antero-lateral ganglionic arteries. 

Section II. — Interior Surface oe the Cerebrum. 

The boundaries of the cerebral ventricles constitute the 
interior surface of the cerebrum. Considering all the cere- 

(66) Trigonum olfactorium. 

(67) Area parolfactoria (Broca). 

(68) Lamina perforata anterior. 



THE CEREBRUM. 2$ 

bral cavities together, we notice that they occupy a wedge- 
Jike space. In shape the wedge is rectangular; and it stands, 
base upward, against the corpus callosum. Its beveled sur- 
faces look toward the hemispheres. The blade is driven 
downward as if to split the cerebrum into lateral halves, the 
edge resting on the medial structures at the base of the brain. 
The space is inclosed laterally between the diverging internal 
capsules, which, within the hemispheres, decussate with the 
lateral .extremities of the corpus callosum. The two struc- 
tures most necessary to an understanding of the cerebral 
cavity, therefore, are the internal capsule 1 and corpus 
callosum. 

Internal Capsule. — Looking at the base of the brain, we 
see two broad bands of nerve fibers ; the crustse, or peduncles, 2 
issue from the front of the pons and, diverging: upward and 
forward, enter the hemispheres beneath the optic tracts. The 
peduncular fibers are reinforced bv additional fibers within 
the hemisphere. The fibers then radiate toward the cerebral 
cortex in the form of a hollow cone or funnel. This funnel- 
like group of fibers is the internal capsule. The bell of the 
funnel opens upward and outward and contains the lenticular 
nucleus; its solid spout, directed toward the pons and 
medially, is the crusta. Antero-inferiorly the fibers in the 
bell of the funnel diverge to opposite sides of the fissure of 
Sylvius and produce a break in its continuity, otherwise the 
funnel is complete. As the internal capsule proceeds into the 
liemisphere, it impales the corpus striatum in such manner 
as to place the caudate nucleus and amygdala upon its cir- 
cumference and to inclose within its walls (to capsula to 1 ) the 
lenticular nucleus. The lenticular nucleus is separated ex- 
ternally from the claustrum by a thin layer of fibers called 
the external capsule. 8 

(1) Capsula Interna. (2) Bases pedunculi. (3) Capsula externa 



26 THE BRAIN AND SPINAL CORD. 

Inferior Lamina. — The internal capsule 4 is flattened from 
above downward. It has, therefore, a superior and an infe- 
rior lamina, which, posteriorly, are continuous with each 
other; but, anteriorly, are separated by the fissure of 
Sylvius. The inferior lamina (or inferior ramus, as seen 
in sagittal section) is a very thin layer and bevels down to a 
sharp edge anteriorly. In front it presents a free border. 
Its fibers pass outward beneath the lenticular nucleus and, 
after winding over the amygdala and the descending horn . of 
the lateral ventricle, terminate in the parietal and temporal 
lobes. It contains part of the temporo-pontal motor tract 
which extends from the temporal cortex to the nucleus of 
the pons ; and also the following sensory fibers, viz., the ansa 
peduncularis (common sensory) running from the thalamus 
to the somaesthetic cortex, and part of the acustic radiations 
(special sensory) which extend from internal geniculate body 
to the auditory cortex in the superior and transverse temporal 
gyri. In the angle between the descending horn and the 
body of the lateral ventricle, the inferior lamina joins the 
superior. 

The Superior Lamina (or superior ramus) of the internal 
capsule contains most of the crusta. It is a thick and strong 
sheet of fibers. Often it is considered as identical with the 
"internal capsule." the inferior lamina being disregarded. 
The superior lamina ascends, fan-like, from the crusta to the 
lateral extremity of the corpus callosum with which it inter- 
crosses. It has a free border anteriorly, though imbedded in 
the corpus striatum. Upon its internal surface rest the optic 
thalamus, below and behind, and the caudate nucleus, above 
and farther forward. It thus separates the optic thalamus 
and caudate nucleus from the lenticular nucleus. A bend 

(4) Capsula interna. 



THE CEREBRUM. 2*] 

near the middle of the superior lamina, called the genu, 
divides it into an anterior 5 and a posterior segment, 6 which 
tend slightly outward from the genu and form an angle with 
each other, open outward, of about 120 degrees. 

Motor Fibers. — The fibers of the genu of the internal 
capsule are very largely motor and constitute the pyramidal 
tract. They may be traced from the Eolanclic area of the 
cortex, through the genu of the internal capsule and middle 
three-fifths of the crusta, and on down into the spinal cord, 
where they end in ramifications about the cell-bodies in the 
anterior horn of gray matter. From these same spinal cell- 
bodies other fibers arise which constitute the motor part of the 
spinal nerves. Fibers of the pyramidal tract also end in the 
mid-brain pons and medulla: their end-tufts are related to 
the nuclear cell-bodies of motor cranial nerves. The anterior 
segment (pars frontalis) of the internal capsule contains a 
motor tract which extends from the prefontal cortex through 
the inner one-fifth of the crusta to the nucleus of the pons 
and motor nuclei of cranial nerves (Flechsig). It is the 
fronto-pontal tract. 7 In the posterior segment (pars occipi- 
talis), behind the pyramidal tract, and also partly in the 
inferior lamina, is another motor tract, described by Flechsig. 
It rises from the temporal cortex and running beneath and 
behind the lenticular nucleus and through the outer one- 
fifth of the crusta, terminates in the nucleus of the pons, 
and also in nuclei of motor cranial nerves (Spitzka). That 
is the temporo-pontal tract. 8 

Sensory Fibers. — In both segments of the internal capsule 
there are common sensory fibers which rise chiefly in the 

(5) Pars frontalis. 

(6) Pars occipitalis. 

(7) Tractus cerebro-corticopontalis frontalis. 

(8) T. cerebro-corticopontalis temporalis. 



28 THE BRAIN AND SPINAL CORD. 

optic thalamus and end in the somaesthetic cortex. They 
constitute the cortical fillet and convey ordinary sensations. 
In the anterior segment is the anterior stalk of the thalamus 
which ends in somaesthetic cortex anterior to the precentral 
fissure. The posterior segment contains the ansa lenticularis 
which conveys ordinary sensations from the thalamus to the 
somaesthetic cortex chiefly in the upper Rolandic area. At 
the junction of the superior and inferior laminae of the 
internal capsule are the special sense fibers. The optic radia- 
tions 9 and auditory radiations 10 occupy the retro-lenticular 
part of the internal capsule. The former extend through it 
from the optic thalamus and external geniculate body to the 
cuneus ; the latter rise in the internal genicu 1 ^e body and 
end in the superior and transverse temporal convolutions. 
Many fibers of the internal capsule give off branches (collat- 
erals) which pass through the corpus callosum to the 
opposite hemisphere; other fibers may be traced entire 
through the same course to the cortical cells of the opposite 
side. 

The superior lamina of the internal capsule, proceeding 
outward and upward into the hemisphere, decussates with 
the corpus callosum and enters into the corona radiata. To- 
gether with the caudate nucleus, optic thalamus and taenia 
semicircularis, which lie on its internal surface, it forms the 
entire lateral boundary of the general cavity of the cerebrum. 
It thus determinates the lateral part of the interior cerebral 
surface. 

Corpus Callosum. — The entire roof of the cerebral cavity, 
representing the base of the wedge, is formed by the corpus 
callosum. A part of the anterior boundary is also formed 

(9) Radiatio occipito-thalamica (Gratioleti). 

(10) Radiatio temporothalamica. 



THE CEREBRUM. 2g 

by it. The corpus callosum is a thick sheet of fibers four 
inches broad, from before backward, which joins the hemi- 
spheres together. It constitutes the great white commissure, 
being composed chiefly of those medullated cortical axones 
which end in arborizations about cortical cells of the opposite 
hemisphere. It contains some fibers which, after passing 
through it, turn down in the internal capsule; and, also, 
collaterals from capsular fibers. The corpus callosum is 
placed nearer to the anterior than the posterior pole of the 
hemispheres. Separating the hemispheres above, it is seen 
in the bottom of the great longitudinal fissure. It is about 
an inch in transverse length. 

The upper surface is concave from side to side; and 
divided, medially, by a longitudinal raphe. Transverse 
stria? are plainly visible. A few longitudinal striae are also 
found running on either side of the raphe, the nerves of 
Lancisi 11 ; and others run near the lateral end of the callo- 
sum. At the anterior and at the posterior border, the corpus 
callosum is bent downward (scroll like) ; hence, it is supe- 
riorly convex from before backward. 

Its inferior surface is concave antero-posteriorly and near 
its posterior border is fused with the body of the fornix. 
Anterior to that fusion, it is joined to the fornix, along the 
median line, by the septum lucidum. 

The posterior border is flexed downward about forty-five 
degrees. Giving passage to the fibers which join the middle 
and posterior parts of the hemispheres, the posterior border 
is the thickest part of the corpus callosum. It is on that 
account called the pad, or splenium. 

The anterior border is bent downward and then backward, 
sweeping through 180 degrees of flexion. It terminates in 
a sharp edge (sharp point, seen in sagittal section) called the 

(11) Striae longitudinales mediates et laterales. 



30 THE BRAIN AND SPINAL CORD. 

rostrum. The rostrum is continuous with the lamina termi- 
nalis at the base of the brain. It sends downward on either 
side a band of fibers, continuous with the nerves of Lancisi, 
which constitutes the peduncle of the corpus callosum. Each 
peduncle, after passing across the anterior perforated lamina, 
ends in the uncus of the hippocampal gyrus. The transverse 
fibers of the rostrum, in the hemisphere, form the floor of 
the anterior horn of the lateral ventricle. 

Genu and Truncus. — The down-turned part of the corpus 
callosum is the genu. It joins the rostrum to the main body, 
the truncus. The genu forms part of the anterior boundary 
of the cerebral cavity; the truncus forms the roof. Fibers 
uniting the frontal lobes of the cerebrum pass through the 
genu, and in the hemisphere, bound the anterior horn of the 
lateral ventricles above and in front. Those fibers arching 
forward and forming the roof of the anterior horn are called 
the forceps minor. The forceps major, composed of fibers 
from the splenium which bend backward into the occipital 
lobe, lies in the roof and inner wall of posterior horn. 

Each lateral extremity of the corpus callosum is overhung 
by the gyrus fornicatus, which covers the lateral longitudinal 
striae (taenia? tectae). 12 Inclosed between the gyrus fornicatus 
and corpus callosum is the fissure-like ventricle of the callo- 
sum, which represents part of the fissura prima of the 
embryo. Under the splenium the fissura prima is continued 
in the hyppocampal fissure. 

The boundaries of the general cavity of the cerebrum may 
be given as follows: 

Roof (base of wedge) — 
Corpus callosum. 

(12) Striae longitudinales laterales. 



THE CEREBRUM. 31 

Floor (edge of wedge) — 
Tegmentum (Mid-brain), 
Posterior perforated lamina (Mid-brain), 
Tuber cinereum, 
Infundibulum, 
Lamina cinerea. 
Lateral wall (beveled surface) — 
Internal capsule, 
Caudate nucleus, 
Taenia semicircularis, 
Optic thalamus. 
Anterior wall (border of wedge) — 
Lamina terminalis, 
Anterior commissure, 
Genu of corpus callosum. 
Posterior wall — 

Corpora quadrigemina (Mid-brain) and 
Posterior commissure (with aqueduct of Sylvius be- 
neath them), 
Pineal body, 
Great transverse fissure, containing the velum interposi- 

tum, 
Splenium (being bent down slightly behind the cavity). 
The cerebral cavity thus bounded is subdivided by two 
partitions. The body of the fornix, together with the velum 
interposition and roof epithelium of the third ventricle, 
forms a horizontal partition which divides the cavity into an 
Tipper and lower chamber. The superior chamber is divided 
into two lateral chambers, the lateral ventricles, by a double 
vertical partition, the septum lucidum. The inferior cham- 
ber is the third ventricle. 



32 THE BRAIN AND SPINAL CORD. 

The body of the fornix 13 is a triangular sheet of fibers, 
whose base is attached to the nnder surface of the spleninm 
of the corpns callosum, and whose bifid apex extends forward 
to the rostrum and to the anterior commissure. Its lateral 
borders rest on the optic thalami, the velum interpositum 
alone intervening. Thus the narrow chamber between the 
optic thalami (the third ventricle) is separated from the 
broader, superior part of the cerebral cavity by the body of 
the fornix. The body of the fornix is produced by the 
Rpproximation of two bundles of white fibers, one belonging 
to each hemisphere. These bundles are the pillars of the 
fornix. . 

The posterior pillar 14 may be traced from the uncus (as 
corpus fimbriatum), and from the hippocampus major up- 
ward through the descending horn and into the floor of the 
body of the lateral ventricle, where it unites with its fellow 
of the opposite side in forming the body of the fornix. At 
the apex of the body of the fornix, which is the anterior 
end, the bundles again separate and become the anterior pil- 
lars. The posterior pillars are united at the back part of 
the body of the fornix by a few transverse and oblique fibers 
which form the lyre, or commissura hippocampi. The com- 
missure is best seen when the corpus callosum and fornix are 
viewed from below; its fibers connect each posterior pillar 
of the fornix with the optic thalamus, hippocampus major 
and uncus of the opposite side. 

The anterior pillars, 15 one on either side, pass down in front 
of the optic thalami, bounding the foramina of Monro; and 
then descend to the corpora albicantia, at the base of the 
brain. On the way down the pillars pass behind the anterior 

(13) Corpus fornicls. 

(14) Crus fornicls. 

(15) Columnse fornicis. 



THE CEREBRUM. 33 

commissure, beyond which each pierces the inner part of the 
optic thalamus of the same side. The fibers of the anterior 
pillars probably terminate in the corpora albicantia, from 
which other fibers take their origin (the bundles of Vicq 
d'Azyr) 16 and ascend to the anterior nucleus of the optic 
thalami. 

The upper surface of the body of the fornix is convex 
from before backward. It forms the postero-median part of 
the floor of the lateral ventricle. Medially, it is joined to 
the corpus callosum by the septum lucidum. 17 

The septum lucidum, a double-walled sagittal partition, 
divides the superior chamber of the cerebral cavity into lateral 
halves, the lateral ventricles. The septum lucidum is cres- 
centic in outline. Its convex border fits, medially, into the 
concave surface of the body, genu and rostrum of the corpus 
callosum. Its concave border rests upon the fornix. Each 
wall of the septum lucidum is a part of the original medial 
wall of the cerebral hemisphere and is, therefore, composed 
of cortical and medullary matter. The walls inclose a part 
of the great longitudinal fissure, called the fifth ventricle. 
That fissure, in embryo, was open down to the velum inter- 
positum on the inter-brain; but its lower part becomes cut 
off and inclosed by the development of the fornix, anterior 
commissure and corpus callosum. The cerebral cavity is 
thus divided into four ventricles, viz. : 

Two lateral (the ventricles of the hemispheres), 

Fifth (the ventricle of the great longitudinal fissure), and 

Third (ventricle of the inter-brain). 

THE FIFTH VENT1UCLE. 

This is the fissural ventricle, or the ventricle o\' the 

(16) Fasciculus thalamo-mamillaris. 

(17) Septum pellucldum. 



34 THE BRAIN AND SPINAL CORD. 

septum. 38 The fifth ventricle is a very narrow, antero- 
posterior cleft between the walls of the septum lucidum, 
with which it coincides in extent. It is situated within the 
concavity of the corpus callosum between the lateral ven- 
tricles, above and anterior to the third ventricle. Below and 
posteriorly it is bounded by the fornix. It is not a part of 
the embryonic brain cavity, but of the great longitudinal 
fissure. Therefore it does not communicate with any other 
ventricle, each of the others being a part of the cavity of the 
neural tube from which both brain and cord are developed. 
Instead of ependyma, which lines other ventricles, the lining 
of the fifth is modified pia mater. A lymph-like fluid fills it. 

THE LATERAL VENTRICLE. 

The hemispheres contain the largest of the six ventricles. 
Situated one on either side of the median line, the ventricles 
of the hemispheres are very naturally called the lateral 
ventricles. 19 Each represents a branch of the cavity of the 
embryonic neural tube. In consequence, the lateral ventricles 
communicate with all others except the fifth. By the fora- 
men of Monro, each directly communicates with the third 
ventricle ; and through that, indirectly, with the fourth and 
sixth. The foramen of Monro 20 is situated between the 
front of the optic thalamus and the anterior pillar of the 
fornix. It extends between the anterior extremity of the 
third ventricle (the aula) and the junction of the anterior 
horn with the body of the lateral ventricle. The lateral 
ventricles are lined with ependyma, which is a transparent 
membrane composed of two layers, viz., neuroglia, with a 
covering of columnar ciliated epithelial cells. Over the optic 

(18) Cavum septi pellucidi. 

(19) Ventricull laterales. 

(20) Foramen interventriculare (Monroi). 



THE CEREBRUM. 35 

thalamus (the part seen in the lateral ventricle) and the 
choroid plexus, the neurogliar layer is absent. 

The lateral ventricle may be studied best in four parts : 
the central part or body ; the anterior, the middle or descend- 
ing, and the posterior cornu. 

The body of the lateral ventricle 21 is the ventricle of the 
parietal lobe of the cerebrum. The following are its 
boundaries : 

Roof — Corpus callosum. 

Floor (from before, backward and inward) — 
Caudate nucleus of the corpus striatum, 
Taenia semicircularis, 
Optic thalamus (covered by epithelium), 
Choroid plexus (covered by epithelium), 
Fornix. 

Medial wall — Septum lucidum. 

External wall — Internal capsule. 

The corpus callosum forms a complete roof for the body 
of the lateral ventricle. The roof inclines upward and out- 
ward from the septum lucidum, the inner wall of the ven- 
tricle, to the superior lamina of the internal capsule, which 
forms its outer wall. The floor of the body of the ventricle 
is formed by the five parts, as named above, which will now 
be considered in the order given. 

Corpus Striatum. — The striated body is the basal ganglion 
O'f the hemisphere. It is an ovoid mass of gray matter im- 
bedded, for the most part, in the cerebral medulla ; but it is 
continuous below with the anterior perforated lamina and 
extends above into the floor of the lateral ventricle. It 
measures two inches from before backward, an inch and a 
quarter transversely and, from above downward, one inch 

(21) Ventriculus lateralis (pars centralis). 



36 THE BRAIN AND SPINAL CORD. 

and a half. It is placed anterior and external to the optic 
thalamus. It is a reddish-gray body and the streaked ap- 
pearance of the corpus striatum is due to the white capsular 
fibers which pierce it. The ' striated body is an important 
way-station in the motor conduction path and perhaps one 
of less importance in the sensory path. The internal capsule 
divides it into two nuclei, namely, the lenticular nucleus 
(extraventricular part), 22 and the caudate nucleus, which is 
seen in the lateral ventricle. Anterior to the free borders 
of the superior and inferior capsular laminae, the two nuclei 
are united with each other, with the anterior perforated 
lamina and with the lower end of the claustrum. 

The lenticular nucleus occupies the cone-like cavity of the 
internal capsule, by whose lamina? it is separated from the 
ventricle. It is shorter fore and aft than the caudate nu- 
cleus. It resembles a biconvex lens with a somewhat thick- 
ened anterior border, when viewed in horizontal section. In 
transverse vertical section through its center, it is triangular 
in shape. The hypotenuse and base are formed, respectively, 
by the superior and inferior lamina? of the internal capsule. 
The external capsule forms the perpendicular and separates 
the lenticular nucleus from the claustrum. The latter is a 
thin sheet of isolated gray matter, found just medial to the 
island of Eeil. In extent and position, fore and aft, the 
island of Eeil and lenticular nucleus coincide. The lenticu- 
lar nucleus is subdivided by two white lamina?., parallel with 
its external surface, into three zones. The outer zone, called 
the putamen, is deeply pigmented, and, like the caudate 
nucleus, is of a reddish-gray color; but the two inner zones, 
having less pigment, are of a pale yellowish tint. They form 
the globus pallidus. 

(22) Nucleus lentiformis. 



THE CEREBRUM. 37 

The nucleus caudatus (the tailed nucleus) is a pear-shaped 
body of reddish-gray color, situated on the perimeter of the 
internal capsule. It is of the intra-ventricular part of the 
striated body and forms a strip of the ventricular floor along 
the outer wall. The bulb 23 of the caudate nucleus is directed 
forward. It is seen in the anterior horn of the lateral ven- 
tricle. From the bulb the nucleus tapers as it proceeds 
backward through the body of the ventricle. Its tail, or 
surcingle, 24 turns downward in the roof of the middle horn, 
and ends in a considerable swelling, called the amygdala, 25 
near the apex of the horn. The caudate nucleus is covered 
on its ventricular surface by ependyma. The opposite sur- 
face, resting against the fibers of the internal capsule, is 
irregular and serrated. 

The taenia semicircularis 26 lies just internal to the nucleus 
caudatus. It is a band of white fibers traversing the floor of 
the body of the ventricle and the roof of its descending horn, 
but covered by the vein of the striate body. It may be said 
to rise from the amygdala. Ascending to the ventricle, it 
passes forward between the caudate nucleus and the optic 
thalamus to the foramen of Monro, where it divides into 
two bundles. One of them joins the anterior pillar of the 
fornix. The other, passing over the anterior commissure, 
terminates in front of it in a mass of cells between the septum 
lucidum and the nucleus caudatus. Perhaps some fibers 
terminate in the latter. 

Optic Thalamus. 27 — A fusiform part of this ganglion ol 
the inter-brain is visible in the floor of the lateral ventricle, 
between the taenia semicircularis and the choroid plexus. It 
extends throughout the ventricular body from the foramen 
of Monro to the descending horn. A transparent Layer o\' 

(23) Caput nuclei caudati. (26) Stria termlnalis. 

(24) Cauda nuclei caudati. (27) Thalamus. 

(25) Nucleus amygdalae. 



38 THE BRAIN AND SPINAL CORD. 

epithelium, extending from the fornix to the taenia semi- 

circularis, and representing the hemisphere wall, covers it. 
The optic thalamus will be described with the third ventricle 
and inter-brain. 

The choroid plexus 28 of the lateral ventricle is the vascular 
border of the velum interpositum. It projects, laterally, 
from beneath the fornix and its posterior pillar into the floor 
of the body of the ventricle and the inner wall of the de- 
scending horn. The epithelium, above mentioned, invests it ; 
and it borders the fornix like a ruffle. It is called choroid 
plexus (chorion , a membrane) because it is membrane-like. 
The anterior choroid artery 29 from the internal carotid and 
the postero-lateral choroid, a branch of the posterior cerebral, 
supply the plexus. The former pierces the temporal lobe 
and enters the apex of the descending horn of the ventricle; 
the latter passes in through the great transverse and choroid 
fissures, following the velum interpositum. The choroid 
vein carries the blood away. At the foramen of Monro, it is 
joined by the vein of the striated body and forms the vein 
of Galen. The vein of Galen 30 courses backward in the 
velum interpositum and unites with its fellow of the opposite 
side; and then the common vein, 31 uniting with the inferior 
longitudinal sinus, forms the straight sinus. 

The floor of the body of the lateral ventricle is completed 
by the superior surface of the fornix. 

The cornua 32 of the lateral ventricle are three in number. 

The anterior cornu 33 projects from the body of the ventricle 
forward and outward around the bulb of the caudate nucleus. 
It is the ventricle of the frontal lobe and is deep and narrow. 
Its boundaries are as follows: 

(28) Plexus choroideus ventriculi lateralis. 

(29) Arteria choroidea anterior. 

(30) Vena cerebri interna, and 31, v. cerebri magna (Galeni). 

(32) Cornua ventriculi lateralis. 

(33) Cornu anterius ventriculi lateralis. 



. THE CEREBRUM. 39 

Roof — Corpus callosum (forceps minor). 

Floor — Bostrum. 

Anterior wall — Genu. 

Inner wall — Septum lucidum. 

Outer wall — Caudate nucleus. 

The posterior cornu 34 is directed backward and downward 
in a curve concave inward, from the ventricular body into 
the occipital lobe. Its extremity bends medially toward the 
calcarine fissure with which the horn is parallel. That fissure 
produces the ridge along the inner wall called the hippo- 
campus minor. 35 The posterior horn is roofed over by fibers 
from the splenium of the corpus callosum, which turn down 
outside the horn and also form part of the external boundary. 
A well-marked bundle of fibers from the splenium, forceps 
major, is found passing along the medial border of the roof 
into the occipital lobe. The white matter of the occipital 
lobe forms the remaining boundaries. The anterior extrem- 
ity of the posterior cornu is continuous, laterally, with the 
beginning of the descending horn. At the junction of the 
two is a triangular area, the trigonum ventriculi. 

The middle, or descending, cornu 36 is the ventricle of the 
temporal lobe. Its course is crescentic as it follows the peri- 
meter of the internal capsule. It first runs outward and 
backward from the body of the ventricle, then it turns 
downward, and finally it proceeds forward and inward 
to within an inch of the apex of the temporal lobe. Tn 
horizontal section just below the general cavity of the 
ventricle, the descending horn is triangular. In that posi- 
tion it has a posterior wall (or floor), an inner wall, and a 
curved antoro-cxtemal wall (or roof), which is continuous 

(34) Cornu nosterius ventriculi lateralis. 

(35) Caloar avis. 

(36) Cornu infcrlus ventriculi lateralis. 



40 THE BRAIN AND SPINAL CORD. 

above with the outer wall and floor of the body of the 

ventricle. 

The parts found in the walls of the descending cornu may 
be enumerated as follows: 

Eoof (or antero-external wall) — 

Pnlvinar of optic thalamus (covered by epithelium), 
Inferior lamina of internal capsule, partially cov- 
ered by surcingle and amygdala of caudate nucleus, 
and taenia semicircularis. 
Floor (or posterior wall) — 
Eminentia collateralis, 
Hippocampus major and pes hippocampi, 
Posterior pillar of fornix and corpus fimbriatum. 
Inner wall (medial) — 

Epithelium (of hemisphere wall) covering, 
Pulvinar, 
Choroid plexus, 
Transverse fissure, and 
Dentate fascia. 
The structures in the roof of the descending horn have 
been sufficiently described. They are easily understood 
when it is recalled that the roof of the horn is continuous 
with the outer wall and floor of the ventricle; the internal 
capsule (inferior lamina), the surcingle and amygdala and 
the taenia semicircularis form it. 

Beginning at the trigonum ventriculi 37 and extending 
along the outer border of the floor to the end of the descend- 
ing horn is a low ridge caused by the collateral fissure. It 
is the eminentia collateralis. In front of it and internal to 
it is a prominent ridge, the hippocampus major, 38 which en- 

(37) Trigonum collaterals 

(38) Hippocampus. 



THE CEREBRUM. 41 

larges downward to a tabulated extremity, called the pes 
hippocampi. 39 The ridge is due to the infolding of the floor 
over the hippocampal fissure on the medial surface of the 
cerebrum. The ventricular surface of the hippocampus 
major is formed by a lamina of white matter, the alveus, 
but the deeper part is cortical matter composed almost en- 
tirely of large pyramidal cell-bodies. The posterior pillar 
of the fornix rests in the concavity of the hippocampus, 
where most of its fibers terminate, but a small bundle of 
them, the corpus fimbriatum, passes beyond it and ends in 
the uncus. 

A layer of epithelium, representing the hemisphere wall, 
forms the floor of the choroid fissure and the whole inner 
wall of the descending cornu. It covers the cushion-like 
projection (the pulvinar) of the optic thalamus, which forms 
a small part of both roof and inner wall. Behind and 
superiorly, it is attached to the pillar of the fornix, from 
which it extends forward and outward to the taenia semi- 
circularis. The epithelium covers the choroid fissure, which 
otherwise would form a communication between the horn 
and the exterior. Through the choroid fissure the border 
of the velum interpositum projects toward the ventricle, and. 
pushing the epithelium before it into the horn, forms the 
chorid plexus. Within the fissure there is a serrated free 
border of cortex called the dentate fascia. 40 The dentate 
fascia folds medially in front of the hippocampal fissure and 
with the hippocampus major forms an S-shaped fold of the 
cortex. The S-shape is perfect in the left hemisphere, when 
viewed with the frontal lobes upward and the convex surface 
of the brain toward the spectator. The top of the letter is 

(39) Diprltationes hippocampi. 

(40) Fascia dentata hippocampi. 



42 THE BRAIN AND SPINAL CORD. 

the fascia dentata; the superior curve is the hippocampus, 
produced by the hippocampal fissure, the upper concavity; 
the lower concavity, open toward the ventricle, is the groove 
beteween the hippocampus major and the eminentia col- 
laterals. 

THE THIRD VENTRICLE AND INTER-BRAIN. 

The inter-brain 41 is medial in position. It is situated 
beneath the fornix and the layer of epithelium extending 
from the border of the fornix to the taenia semicircularis. 
The velum interpositum only intervenes between them. 
Laterally, it is bounded by the superior laminae of the in- 
ternal capsules. The ventricle of the inter-brain is the 
third 42 in number. The third ventricle, therefore, is 
medially located; and is at a lower level than the ventricles 
of the hemispheres. Through the foramina of Monro, its 
anterior part (the aula) communicates with each lateral 
ventricle, and the aqueduct of Sylvius connects it, behind, 
with the fourth ventricle. The third ventricle is fissure-like. 
It is a narrow, vertical cleft about an inch in length from 
before backward and a quarter of an inch broad at its widest 
part. It separates the optic thalami, and extends almost to 
the inferior surface of the cerebrum. The roof follows the 
curve of the fornix and arches from the posterior commis- 
sure forward to the anterior commissure. The anterior wall 
extends from the upper border of the anterior commissure 
down to the optic recess, at the angle of flexion in the lamina 
cinerea. The floor describes two arches, convex toward the 
ventricle. The first arch, very convex and short, stretches 
between the optic recess and the inf undibulum in which the 
floor reaches its lowest point. The distance from the in- 

(41) Diencephalon. 

(42) Ventriculus tertius. 



THE CEREBRUM. 43 

fundibulum to the anterior orifice of the aqueduct of Sylvius 
is spanned by the second arch. It is long and rather flat. 
Its posterior extremity is but a sixteenth of an inch below 
the posterior commissure; the anterior orifice of the Sylvian 
aqueduct separates them. The ventricle is thus contracted 
behind to the size of the Sylvian aqueduct with which it is 
continuous. The lateral walls are close together through- 
out. At one point near the middle they come together and 
are joined by the gray, or middle, commissure. 43 Antero- 
superiorly, the lateral wall is perforated by the foramen of 
Monro. 44 That foramen constitutes the slight separation 
between the front of the optic thalamus and the anterior 
pillar of the fornix. It opens into the lateral ventricle at 
the junction of the anterior horn with the body. The epen- 
dyma which lines the third ventricle is continuous through 
the foramen of Monro with the lining of the lateral ventri- 
cle. But one layer of the ependyma is present in the roof 
of the ventricle ; that is the epithelial layer. The third ven- 
tricle, like all true ventricles, is occupied by cerebro-spinal 
fluid. 

The following are the boundaries of the third ventricle: 
Roof- 
Posterior commissure, 
Roof epithelium and pineal body, 
Velum interpositum and choroid plexuses, 
Fornix. 
Anterior wall — 

Epithelium, covering 

Pillars of fornix and anterior commissure. 
Lamina terminalis. 



(43) Massa intermedia. 

(44) Foramen interventriculare. 



44 THE BRAIN AND SPINAL CORD. 

Floor- 
Lamina cinerea and optic commissure, 

Tuber cinereum and infundibulum, 

Corpora albicantia, 

Posterior perforated lamina (of mid-brain), 

Tegmentum (of mid-brain) . 
Posteriorly — 

Ventricle is continuous with aqueduct of Sylvius. 
Lateral walls — 

Optic thalamus, 

Anterior pillar of the fornix, and 

Foramen of Monro between them. 
Roof. — A band of white fibers passes across the back part 
of the third ventricle and supports the posterior end of the 
roof epithelium. That band is the posterior com- 
missure. 45 It crosses immediately in front of the cor- 
pora quadrigemina. Beneath it is the anterior orifice of 
the aqueduct of Sylvius. The pineal body is above and 
behind it, and the commissure is inclosed between the ven- 
tral and dorsal pineal laminae. The posterior commissure 
stretches from one optic thalamus to the other; but most 
of its fibers terminate in the parieto-occipital region. It 
contains four sets of fibers, viz.: (1) Commissural fibers 
between the optic thalami ( ?) ; (2) the upper decussation 
of the posterior longitudinal bundles; (3) some fibers from 
the pineal stria, derived from the optic tract near the ex- 
ternal geniculate body, which cross to the opposite nucleus 
(upper part) of the motor oculi (Darkschewitsch) ; and, 
(4) fibers from the fillet crossing to the opposite hemisphere. 
The roof epithelium of the third ventricle stretches from 
the posterior commissure to the anterior commissure and, 

(45) Commissura posterior. 



THE CEREBRUM. 45 

laterally, is attached to the upper internal border of the 
optic thalamus. It is the superficial layer of the ependyma; 
but it is, here, the only adult representative of the roof of the 
neural tube (the thalamencephalon). Anteriorly, this same 
epithelium investing the anterior commissure and pillars 
of the fornix, is the only representative of the neural wall 
(prosencephalon) down to the lamina terminalis. The roof 
epithelium presents two longitudinal folds suspended in the 
ventricle. The lower layer of the velum interpositum. invests 
the epithelium superiorly and the two structures constitute 
the anterior choroid tela; 47 and then, dipping down 
into the longitudinal folds, that- inferior layer of the velum 
interpositum forms the choroid plexuses 48 of the third ventri- 
cle, which are continuous with those of the lateral ven- 
tricles through the foramina of Monro. At the back part 
in the middle line, there is a pouch-like evagination of the 
roof epithelium in the embryo, which develops into the 
pineal body. 

Pineal Body, or Conarium. — It is a cone-shaped body, 49 
a quarter of an inch high and one-sixth of an inch in diam- 
eter, joined to the roof of the third ventricle by a flattened 
stalk or peduncle. 50 It is also called the epiphysis. The 
pineal body is situated in the floor of the great transverse 
fissure, directly below the splenium of the corpus callosum, 
and rests between the superior quadrigeminal bodies on the 
dorsal surface of the mid-brain. It is closely invested by 
pia mater. The pineal stalk 2 splits into a dorsal and a 
ventral lamina. The ventral lamina, passing behind the 
posterior commissure disappears beneath it; but the dorsal 

(47) Tela choroidea ventriculi tertii. 

(48) Plexus choroldeus ventriculi tertii. 

(49) Corpus pineale. 

(50) Habenula. 



46 THE BRAIN AND SPINAL CORD. 

stretches forward over the commissure in continuity with 
the roof epithelium. The borders of the dorsal lamina are 
thickened, pineal striae, 51 and contain fibers which, running 
forward, join the anterior pillar of the fornix. The pineal 
stria? also contain optic fibers which pass through the pos- 
terior commissure to the nucleus of the oculomotor nerve. 

The interior of the pineal body is made up of closed fol- 
licles surrounded by ingrowths of connective tissue. The 
follicles are filled with epithelial cells mixed with calcareous 
matter, the brain-sand (acervulus cerebri). Calcareous de- 
posits are found also on the pineal stalk and along the 
choroid plexuses. The function of the pineal body is un- 
known. It is supposed to represent a cyclopian eye. In 
the Hatteria, a New Zealand lizard, it projects through the 
parietal foramen and presents an imperfect lens and retina 
and, in its long stalk, nerve fibers. 

The velum interpositum, a double triangular fold of pia 
mater, is interposed between the epithelium of the third 
ventricle and the medial part of the floor of the two lateral 
ventricles. Its apex is just behind the anterior commis- 
sure, and its base, directed backward, is continuous, by the 
upper layer, with the pia of the occipital lobes; and, by the 
inferior layer, it is continuous with the pia on the dorsal 
surface of the mid-brain and cerebellum. Each border con- 
stitutes the choroid plexus of the lateral ventricle, and is 
seen (through the epithelium) in the floor of its body and 
along the inner wall of its descending horn. Medially, the 
inferior lamina of the velum interpositum invests the roof 
epithelium of the third ventricle, forming the anterior, or 
superior, choroid tela ; 52 and, laterally, it covers the medial 
half of the upper surface of each optic thalamus. It forms 

(51) Stria medularis thalami. 

(52) Tela choroidea ventriculi tcrtiL 



THE CEREBRUM. 47 

the two choroid plexuses of the third ventricle, 53 which de- 
pend from its medial portion. Between the inferior and 
superior lamina is enclosed some arachnoid tissue; and the 
veins of Galen pass back through it from the foramina of 
Monro to the tentorium cerebelli, where they join with the 
inferior longitudinal sinus in forming the straight sinus. 

Anterior Wall.— The anterior commissure 54 is a very dis- 
tinct round bundle of white fibers about an eighth of an 
inch in diameter. It is seen in the anterior wall of the third 
ventricle supporting the roof epithelium. The epithelium 
there bends down between the pillars of the fornix and in- 
vests the ventricular surface of the commissure. The an- 
terior commissure rests upon the upper extremity of the 
lamina terminalis, between the pillars of the fornix, behind, 
and the rostrum of the corpus callosum, in front. With the 
last two structures it is developed from the hemisphere 
vesicles. It is the most important connecting link between 
the hemispheres in vertebrates without a corpus callosum fall 
below mammals). Bending shortly backward the anterior 
commissure pierces the inferior part of the globus pallichis 
and then radiates toward the cortex, some of its fibers en- 
tering the external capsule. Tt contains two groups of 
fibers: (1) the anterior group, 55 which is the commissure 
of the rhinencephalon, called the pars olfactoria : anrl (2) 
the posterior group, 56 the pars oocipito-tomporalis. The 
former connects the limbic lobes and joins each to the oppo- 
site olfactory tract; the latter euds in the inferior part of 
the occipital and in the temporal cortex. Tn man it is larjreT 
than the pars olfactoria. The upturned part of the lamina 

(53) Plexus choroldea ventrleul! tertH. 

(54) Cornmlssura anterior (cerebri). 

(55) Pars anterior. 

(56) Pars posterior. 



48 THE BRAIN AND SPINAL CORD. 

cinerea, called lamina terminalis. extends from the anterior 
commissure and rostrum of the corpus callosum down to the 
flexure which incloses the optic recess; it completes the an- 
terior boundary of the third ventricle. 

The floor is very narrow. It is formed by the interpe- 
duncular structures plus the tegmentum, namely: lamina 
cinerea (with optic chiasma below it), tuber cinereum and 
infundibulum, corpora albicantia, posterior perforated 
lamina and the tegmentum. The last two are the middle 
and dorsal portions of the mid-brain; the others belong to 
the inter-brain, and all extend laterally beneath the optic 
thalami. The corpora albicantia, located on either side of 
the median line, may be excepted from the ventricular floor, 
as they are directly beneath the thalami (see base of 
cerebrum). 

The third ventricle has its lateral wall formed by the 
optic thalamus and the anterior pillar of the fornix. The 
pillar of the fornix, diverging from its fellow, proceeds down- 
ward and backward to the corpus albicans through the 
medial part of the thalamus. In the ventricle it is covered 
by the ependymal epithelium. It bounds the foramen of 
Monro in front. 

Optic Thalamus.— It is the great ganglion of the inter- 
brain. The thalamus (Thalamos, a bed) 57 is an import- 
ant sensatory way-station. In it or in the hypothalamic nuclei 
almost every impulse of general sensation, in its journey to 
the cerebral cortex, is transferred to a higher neurone. The 
third ventricle separates the thalamus from its fellow, ex- 
cept at the mid-point where they are joined by the middle 
(gray) commissure. 58 The thalamus is situated behind and 
medial to the corpus striatum, and projects backward over 

(57) Thalamus. (58) Massa intermedia. 



THE CEREBRUM. 49 

the superior surface of the mid-brain. Laterally, it rests 
against the superior lamina of the internal capsule, which 
separates it from the lenticular nucleus. The optic thal- 
amus is shaped like an egg with the small end directed for- 
ward. It has an anterior and a posterior extremity and four 
surfaces : superior, inferior, internal and external. 

Extremities. — The anterior, extremity of the thalamus is 
lost in a large group of fibers (anterior stalk) which, run- 
ning through the anterior segment of the internal capsule, 
ends in the gyrus fornicatus and the frontal lobe of the 
cerebrum. - 

The posterior end presents a large pillow-like prominence, 
the pulvinar; and beneath it is a smaller swelling, which 
forms the lowest point of the thalamus, the external geni- 
culate body. The internal geniculate body (of the mid- 
brain) is also continuous with this extremity internal to the 
pulvinar. The two geniculate bodies constitute the meta- 
thalamus. 

Surfaces.— -The internal, or medial, surface of the optic 
thalamus forms the lateral wall of the third ventricle. It 
is joined to the internal surface of the opposite thalamus by 
the middle commissure. Both this and the superior surface 
are composed of a thin lamina of longitudinal white fibers, 
the stratum zonale. 

The superior surface of the thalamus is divided by an 
oblique groove, the choroid groove, corresponding in posi- 
tion to the border of the fornix, into two areas. The area 
inside the groove is covered by the velum interpositum and 
the fornix. Infernally, it is bounded by the pineal stria and 
attachment of the roof epithelium, Posteriorly, next the 
stria, is a triangular depression bounded, behind, by a 
transverse groove in front of the corpora quadrigemina. and 



50 THE BRAIN AND SPINAL CORD. 

by a slight groove, the sulcus habenulse, externally. That 
depressed surface is called the trigone of the habenula. 59 
Beneath the triangle is one of the thalamic nuclei. The 
outer area is seen in the floor of the lateral ventricle. It 
presents an anterior elevation, the anterior tubercle, 60 be- 
neath which is the anterior nucleus of the thalamus. A 
sheet of epithelium, extending from the fornix to the taenia 
semieircularis, covers this outer area and separates it from 
the ventricular cavity. 

A special lamina of fibers, the external medullary 
lamina, derived from the fillet, forms the external surface 
of the optic thalamus and rests upon the superior lamina 
of the internal capsule. 

The inferior surface blends with the superior surface of 
the tegmentum and substantia nigra, and forms the laminae 
and nuclei of the tegmental region. (See below). 

Hypothalamic tegmental region 61 is composed of three 
layers: (1) Stratum dorsale next the optic thalamus; (2) 
Zona incerta, the middle; and (3) the nucleus of Luys, or 
hypothalamic body, the inferior. The nucleus of Luys 62 
is but the terminal part of the substantia nigra. The 
reticular formation of the tegmentum, continuing beneath 
the optic thalamus, forms the zona incerta. The stratum 
dorsale is made up as follows: (a) Fibers from the posterior 
longitudinal bundle (Meynert) ; (b) the superior peduncle 
of cerebellum (Forel), among which is the upper end of 
the red nucleus 63 of the tegmentum; and (c) the fillet. 64 

The external geniculate body (geniculum, a little knot or 

(59) Trig-onum habenulae. 

(60) Tuberculum anterius thalami. 

(61) Hypothalamus. 

(62) Nucleus hypothalamicus. 

(63) Nucleus ruber. 

(64) Lemniscus. 



THE CEREBRUM. 5 I 

knee) 65 forms a slight swelling at the lowest point of the 
optic thalamus. It marks the apparent end of the outer 
root of the optic tract and is the terminal nucleus of eighty 
per cent of its fibers. It is joined to the anterior quadri- 
geminal body by the anterior brachium. In appearance 
it is dark colored and laminated; its gray matter, which con- 
tains pigmented multipolar cell-bodies, is divided into thick 
layers by thin laminae of fibers from the optic tract. The 
processes of the multipolar cell-bodies help to form the optic 
radiations. 

The internal geniculate body 66 belongs to the mid-brain. 
It is placed at the end of the inner root, as the external genic- 
ulate is at the end of the outer root, of the optic tract. It 
rises up from the groove between the optic thalamus and cor- 
pora quadrigemina, and is joined to the posterior quadri- 
geminal body by the posterior brachium. The anterior bra- 
chium sweeps around it in front, passing between it and the 
external geniculate body. The internal geniculate body is 
gray in color and is not laminated. Its cell-bodies are small, 
and fusiform in shape. They perhaps give origin to the 
intercerebral fibers (Gudden) of the optic tract and to a 
large number of the acoustic radiations. 

(65) Corpus geniculatum laterale. 

(66) Corpus geniculatum mediale. 



CHAPTER III. 



MID-BRAIN. 



The brain just behind the cerebrum is the mid-brain. 1 It 
is the connecting link between the inter-brain and the hemi- 
spheres, in front, and the pons, behind. This has suggested 
the name isthmus, sometimes applied to it, though isthmus is 
more specifically applied to the constriction behind the cor- 
pora quadrigemina. It is developed from the middle of the 
five brain vesicles, the mesencephalon. The cerebral hemi- 
spheres almost conceal it from view; they overhang it dor- 
sally, and the temporal lobes, inclosing it between them, bend 
medially and cover part of its ventral surface. Only the 
median part of the ventral surface is visible in the complete 
brain. The form of the mid-brain resembles a flattened 
cylinder. Its axis, a half inch long, is pointed upward and 
forward, and its long diameter, which varies from an inch 
to an inch and a quarter in length, is directed transversely. 

surfaces. 

The mid-brain has four surfaces, viz., the ventral and 
dorsal which are free, and the superior and inferior, repre- 
senting the ends of the cylinder, which are attached. The 
two latter are parallel with each other and are formed by 
section. 

The superior surface, sloping downward and forward, 
meets the ventral surface at an acute angle. Its inclination 
is that of the back part of the floor of the third ventricle. 

(1) Isthmus rhombencephali and mesencephalon. 



MID-BRAIN. 53 

External to the floor of the ventricle, it is attached to the 
optic thalami and internal capsules. The blending of it 
with the thalami forms the structures of the hypothalamic 
tegmental regions, and the continuations of the extreme lat- 
eral portions, the crustae, constitute the superior laminae 
of the internal capsules of the hemispheres. In the median 
line behind the third ventricle it is attached to the posterior 
commissure. 

The inferior surface joins the upper surface of the pons. 
It is a little narrower than the superior surface. - It is about 
one inch broad and measures three-quarters of an inch dorso- 
ventrally. 

The ventral surface of the mid-brain looks downward and 
forward. It is deeply grooved longitudinally by the median 
sulcus, 2 and is slightly concave from above downward. It 
is separated on either side from the dorsal surface by the 
sulcus lateralis. 3 Though partially concealed by the tem- 
poral lobes of the cerebrum, the ventral surface is unat- 
tached. It is formed by a prominent band, the crusta, 4 at 
either side; and by a median structure, the posterior per- 
forated lamina, 5 which is inclosed between the two crustae. 
The posterior perforated lamina forms the floor of the 
median sulcus. The inner border of the crusta is free and 
overhangs the perforated lamina slightly. Thus is formed 
the oculo-motor groove between the crusta and perforated 
lamina, whence the third cranial nerve takes its superficial 
origin. The fourth nerve courses forward over the ventral 
surface, but is not attached to it. 



(2) Fossa interpeduncularis. 

(3) Sulcus lateralis mesencephali. 

(4) Basis pedunculi. 

(5) Sustantia perforata posterior. 

(6) Sulcus nervi oculomotorii. 



54 THE BRAIN AND SPINAL CORD. 

The dorsal surface of the mid-brain, though free, is en- 
tirely concealed by the cerebral hemispheres. It forms part 
of the floor of the great transverse fissure and is covered by 
pia mater. The lateral sulcus bounds it on each side. From 
the sulcus lateralis it elevates abruptly toward the median 
line where it presents a longitudinal groove. This produces 
two ridges which are subdivided by a transverse groove into 
the four eminences (colliculi) of the corpora quadrigemina. 
On either side, anterior and a little external to the quadri- 
geminal bodies, is the internal geniculate body. There are 
thus presented six eminences on the dorsal surface of the 
mid-brain. The entire dorsal surface is formed by the 
tegmentum. 

INTERIOR. 

The mid-brain is made up of three great divisions, namely : 
(1) The ventral part, composed of the two crustae; 

(2) the substantia nigra, which is the middle part; and 

(3) the dorsal part, called the tegmentum, composed of lat- 
eral halves united by a raphe. 

The crustae 7 are two rounded bands of white fibers, limited 
by the medial and the lateral sulci, which form the ventral 
part of the mid-brain. They are in contact at the front of 
the pons from which they diverge upward and forward and 
pierce the inferior surface of the cerebrum beneath the optic 
tracts. Entering the cerebrum just external to the optic 
thalamus, the fibers of each crusta spread out, fan-like, in 
the internal capsule. Excepting the medial fillet, a part of 
which enters the inferior lamina, and a part of the temporal 
cerebro-corticopontal tract which takes the same course, the 
crusta enters only into the superior lamina of that inner 
capsule. 

(7) Basis pedunculi (sins.)* 



MID-BRAIN. 55 

The deep portion of the crustae is occupied by the inter- 
mediate bundle, whose fibers arise in the corpus striatum and 
terminate in the nucleus pontis (Flechsig). The superficial 
portion should be studied in three parts: 

(1) The outer fifth of each crusta, the temporal cerebro- 
corticopontal tract, is composed of efferent fibers which 
rise in the temporal cortex, in the superior, middle and in- 
ferior gyri (Dejerine). Proceeding through the inferior 
lamina and the occipital segment of the superior lamina of 
the internal capsule, and through the lateral part of the 
crusta, they terminate chiefly in the nucleus of the pons; a 
few end in motor nuclei of cranial nerves (Spitzka). The 
fibers are probably interrupted in the thalamus or lenticular 
nucleus. They form a segment of the indirect motor path. 
These fibers are medullated later than the pyramidal tract 
(Flechsig). 

(2) The middle three-fifths of the crusta is for the most 
part motor. It is called the pyramidal tract. 8 Its fibers 
rise in the Eolandic area of the cerebral cortex; they form 
the genu and anterior two-thirds of the posterior segment of 
the internal capsule, the middle three-fifths of the crusta, 
the ventral longitudinal fibers of the pons, and the pyramid 
of the medulla. Below the medulla they are continued in 
the direct and crossed pyramidal tracts of the spinal cord. 
Those fibers of the p}^ramidal tract which innervate the mus- 
cles of speech and of the face run through the genu of the 
internal capsule and constitute the medial portion of the 
tract. Immediately behind the face fibers, in the capsula 
interna, and external to them, in the tract, are fibers which 
innervate the muscles of the arm. Still behind these, in the 
internal capsule, and external to (hem in the pyramidal 

(8) Fasciculus longitudinalis pyramidalls. 



$6 THE BRAIN AND SPINAL CORD. 

tract of the crusta, are fibers for the innervation of the trunk 
and leg muscles, the leg fibers being most posterior and most 
external. Intermingled with the pyramidal fibers are a few 
fibers from the cerebellum. The cerebellar fibers, upon 
reaching the pons through the middle peduncle of the cere- 
bellum, ascend with the ventral longitudinal fibers of the 
pons and are sparsely scattered throughout the crusta. 

(3) The inner fifth of the crusta is composed of the 
medial fillet, and the frontal cerebro-corticopontal tract. 
The origin of the latter is probably in the pre-Eolandic cor- 
tex, at the anterior end of the first frontal and at the feet 
of the second and third frontal gyri; and, perhaps, in the 
middle of the gyrus fornicatus. It is motor. This motor 
tract is contained in the anterior segment of the upper 
lamina of the internal capsule. Its termination is in the 
nucleus of the pons and in the motor nuclei of cranial nerves 
( Flechsig) . It constitutes a stage of an indirect motor path, 
like the fibers of the outer fifth of the crusta. and the indirect 
path is continued to the opposite half of the cerebellum by 
neurones whose cell-bodies are in the nucleus pontis 
(Flechsig). The medial fillet 9 (sensory) exists as a dis- 
tinct bundle in this part of the crusta. Superiorly, it enters 
the hypothalamic region, and ends in the ventro-lateral 
nucleus of the optic thalamus. A few of its fibers join the 
ansae lenticularis et peduncularis and run uninterrupted to 
the cortex; they form a part of the inferior lamina of the 
internal capsule, and then, of the medullary lamina? of the 
lenticular nucleus. The medial fillet is the afferent cerebral 
tract of the spinal and of all the cranial nerves with the ex- 
ception of the cochlear division of the auditory. 

The Substantia Nigra. — The central part of the mid-brain 

(9) Lemniscus medialis. 



MID-BRAIN. 57 

is a sheet of pigmented gray matter. The substantia nigra 
is visible at the base of the brain between the crustse, where 
it is called the posterior perforated lamina/ and its margin 
comes to the surface in each lateral sulcus. Antero-pos- 
teriorly, it extends from the pons forward to the corpora 
albicantia and nucleus of Luys. Dorsal to it is the teg- 
mentum. Transversely, the substantia nigra is convex down- 
ward, but it is slightly concave, longitudinally. The third 
nerve pierces it and comes out through the oculomotor 
groove. It contains small pigmented multipolar cell-bodies 
some of which constitute a relay for certain fibers of the 
medial fillet (Barker). There is an aggregation of these 
cells located medially just in front of the pons, the inter- 
peduncular ganglion. 11 According to Forel this ganglion is 
connected by a bundle of fibers, the fasciculus retroflexus, 
with the nucleus habenulas of the optic thalamus. The an- 
tero-lateral portion of the substantia nigra forms the nucleus 
of Luys, or nucleus hypothalamics, on either side. The 
nucleus Luysi lies ventro-lateral to the red nucleus, 12 and is 
separated from it by the zona inserta. 

The Tegmentum.— The dorsal division of the mid-brain, 
being the largest and covering the other two divisions, is 
in consequence called the tegmentum (the cover). It fits 
ventrally into the con-cavity of the substantia nigra, and is 
bounded by the lateral sulcus on each side. Dorsallv. it pre- 
sents the internal geniculate bodies and the corpora quadri- 
gemina. The tegmentum is very thick medially. Tn trans- 
verse section it has a pentagonal form, the curve of (lie sub- 
stantia nigra representing two sides. Superiorly, the an- 
terior extremity of the tegmentum blends with the optic 

(10) Substantia perforata posterior. 

(11) Ganglion interpedunculare. 

(12) Nucleus ruber. 



58 THE BRAIN AND SPINAL CORD. 

thalami in the hypothalamic regions. The tegmentum is 
continuous with the pons behind (caudalward). It contains 
the cavity of the mid-brain, the aque ductus Sylvii. 13 

The Aqueduct of Sylvius. — The aqueduct is a very slender 
canal connecting the third and fourth ventricles. So it is 
the "iter a tertia ad quartum ventriculum." It is situated 
near the dorsal surface of the tegmentum, directly beneath 
the sulcus longitudinalis. It is a half-inch long. In shape 
it is V-like, above; elliptical, in the middle, with a vertical 
major axis; and T-form, below, where it joins the fourth 
ventricle. Its height varies between a sixteenth and an 
eighth of an inch. Like other ventricles it is lined with 
ependyma. A layer of gray matter, thickest on the sides 
and floor, surrounds the aqueduct of Sylvius. It is con- 
tinuous with the gray matter of the fourth ventricle. In it 
are the nuclei of the oculomotor (third) and the trochlear 
(fourth) cranial nerves. 

Nuclei of the Third and Fourth Cranial Nerves. — Both 
nuclei extend the entire length of the aqueduct, and the 
oculomotor (third) 14 is prolonged into the wall of the third 
ventricle, where it receives a bundle of fibers from the op- 
posite pineal stria and optic tract. The nuclei are composed 
of several elongated masses of gray matter, which contain 
cell-bodies of various sizes. They lie side by side in each 
half of the floor of the aqueduct, and are associated with the 
optic tract (external root) by fibers in the posterior commis- 
sure and by association neurones in the anterior quadri- 
geminal bodies. By this connection certain reflex ocular 
movement, accommodation for distance and pupillary con- 
traction are accomplished. The oculomotor (third) nucleus 
is next the median line and behind unites with its fellow 

(13) Aqueductus cerebri. (14) Nervus oculomotorlus. 



MID-BRAIN. 59 

across it. For the most part the third nerve, motor oculi, 
rises from the nucleus of the same side; but it also contains 
crossed fibers from the opposite nucleus and from the pos- 
terior longitudinal bundle of the opposite side. Some of the 
last are derived from the nucleus of the abducent (sixth) 
nerve and, after crossing to the third nerve, help it to supply 
the internal rectus of one eye-ball; while the sixth, rising 
from the same nucleus, supplies the external rectus of the 
other eye. Thus is conjugate deviation accounted for. The 
third nerve passes down to the oculomotor groove through 
tegmentum and substantia nigra. The root fibers of the 
fourth nerve, trochlear (patheticus) 15 proceed dorsally and 
caudalward from the nucleus. They decussate with the 
fibers from the opposite nucleus in the superior medullary 
velum (the valve of Vieussens), from which they emerge on 
either side of the frenulum. They then continue in the op- 
posite nerve around the side and over the ventral surface of 
the mid-brain. The nucleus of the trochlear nerve (also the 
abducent) likewise receives impulses from the optic tract. 

The corpora quadrigemina are four bodies (colliculi) 
which stand upon the quadrigeminal lamina and constitute 
a large part of the dorsal surface of the mid-brain. They are 
seen in the floor of the great transverse fissure, invested by 
pia mater and overhung, anteriorly, by the pineal body. The 
crucial groove separates them and marks out a larger anterior 
pair, 16 elongated from before backward, and a hemispherical 
posterior pair. 17 The internal geniculate body lies in front 
and a little external to the corpora qiiadrigemina. A ridge 
made up of white fibers, the anterior brachium/ 8 joins each 

(15) N. trochlearis. 

(16) Colliculi anteriores. 

(17) Colliculi posteriores. 

(18) Brachium quadrig-oniinum suporius. 



60 THE BRAIN AND SPINAL CORD. 

anterior qua (Trigeminal body to the corresponding external 
geniculate body, sweeping around the internal geniculate 
body in front and externally. The posterior brachium 19 
forms an oblique ridge between the posterior quadrigeminal 
body and the corpus geniculatum internum of the same side. 
The superior peduncle of the cerebellum and lateral fillet 20 
form two ridges which end at the back of each posterior 
quadrigeminal body. The corpora quadrigemina (anterior 
colliculi) constitute the great center for the association of 
ocular movements and reflexes with optic and auditory im- 
pulses and impulses of common sensation. The posterior 
colliculi constitute a relay, or way-station, in the auditory 
path. 

Structure. — The corpora are composed chiefly of gray mat- 
ter. The upper and lower fillet and the valve of Vieussens 
form a layer of fibers, the quadrigeminal lamina, upon which 
they rest and which separates them from the gray matter 
around the aqueduct of Sylvius. They also contain many 
fibers in their interior and are covered, superficially, by a 
thin layer of white matter. (See quadrigeminal bodies, 
Chapter IV). 

The internal geniculate bodies 21 form a part of the teg- 
mentum. They are derived from the mesencephalon with 
the remainder of the mid-brain to which they belong ; but for 
convenience, they were considered with the external genicu- 
late bodies under the heading "inter-brain," which see. The 
internal geniculate bodies form the relay in the auditory path 
next above the posterior quadrigeminal bodies. 

Fibers of the Tegmentum. — The tegmentum is a continua- 
tion of the dorsal longitudinal fibers and the formatio reticu- 

(19) B. quadrigeminum inferius. 

(20) Lemniscus lateralis. 

(21) Corpus geniculatum mediale (sing.). 



MID-BRAIN. 6l 

laris of the pons, and of the gray matter in the floor of the 
fourth ventricle; and, in addition, has the geniculate and 
quadrigeminal ganglia forming its dorsal portion. It is 
composed of symmetrical halves united by a median raphe. 
Each half contains innumerable transverse and longitudinal 
fibers with small masses of gray matter in the meshes. In- 
tersecting the many transverse fibers are six distinct bundles 
of longitudinal fibers. They are continued up through the 
pons, from the cerebellum and the medulla. Those six 
bodies are as follows: 

(1) The Posterior Longitudinal Bundle 22 lies beside the 
raphe, just ventral to the gray matter of the Slyvian aque- 
duct. It is traceable from the anterior cornu of gray mat- 
ter in the spinal cord where its ascending fibers rise 
(Tschermak). Being chiefly an association tract, it receives 
fibers, in the pons, from the cerebellum; and from nuclei of 
the cranial nerves, in the medulla, pons and mid-brain. 
Among the latter are fibers from the sixth to the third nerve. 
It contains also descending fibers which include those from 
the nucleus of the motor oculi to the genu of the seventh, or 
facial, nerve. These latter supply the frontalis, pyramidalis 
nasi, orbicularis palpebrarum and corrugator supercilii mus- 
cles. Through the raphe the posterior longitudinal bundle 
partially decussates with its fellow (lower decussation). 
Many of these fibers pass into the opposite third and fourth 
and other motor cranial nuclei. The remainder of the 
bundle, decussating through the posterior commissure 
(upper decussation) ends in the pineal body and stratum 
dorsale of the hypothalamic region. It connects the cere- 
bellum with opposite nuclei of the cranial nerves and the 
latter with each other. It associates the motor oculi with 

(22) Fasciculus longitudinalis medlalis. 



62 THE BRAIN AND SPINAL CORD. 

the abducent and facial nerves, and the optic with the ab- 
ducent. It also associates spinal and cranial nerves. 

(2) Anterior Longitudinal Bundle. — Just ventral to the 
posterior longitudinal bundle is the fasciculus from the an- 
terior corpus quadrigeminum to the ciliospinal centers in 
the cord. It is the pupillo-dilator tract. 

(3) The Fillet. — Near the upper end of the pons, in the 
ventral part of the formatio reticularis, the fillet, or lemnis- 
cus, forms a very broad band of fibers on either side of the 
median raphe. The fillet is equal in width to half the trans- 
verse diameter of the mid-brain. It continues into the ven- 
tral portion of the tegmentum, but immediately divides into 
two fasciculi, viz., the interolivary fillet, 23 and the lateral, 
or lower, fillet. 24 Farther forward a small bundle leaves the 
lateral part of the interolivary fillet and runs up to the 
superior quadrigeminal body. That bundle is called the 
superior fillet, 25 and what remains is the medial fillet. 26 

Function. — The fillet forms a segment in the direct sen- 
sory tract. It carries impulses from the medulla to the cor- 
pora quadrigemina and optic thalamus. 

Interolivary Fillet. — The fibers composing the inter- 
olivary fillet rise chiefly in the nucleus gracilis and nucleus 
cuneatus of the opposite side of the medulla oblongata. They 
cross over in the sensory decussation of the medulla; and, 
excepting a small bundle, terminate in the ventro-lateral 
nucleus of the optic thalamus. Fibers are added from 
masses of gray matter along the whole course of the inter- 
olivary fillet, especially from the terminal nuclei of sensory 

(23) Lemniscus interolivaris (comprising L. medialis and L. su- 
perior). 

(24) Lemniscus lateralis. 

(25) Lemniscus superior. 

(26) Lemniscus medialis. 



MID-BRAIN. 63 

cranial nerves; and others, also, from the cerebellum. On 
the other hand, certain fibers leave the fillet and end in the 
nuclei along its course, that is, are interrupted, and other 
fibers continue in their stead. A small bundle of fibers 
separating from the lateral part of the interolivary fillet and 
running to the superior quadrigeminal body, forms the 
superior- fillet. It associates ocular movements with sensa- 
tions from cranial and spinal nerves. The medial fillet 
bends ventrally as it runs through the mid-brain. It pierces 
the substantia nigra, in which it undergoes a partial relay, 
and then continues forward, with the inner fifth of the 
crusta, to its termination in the thalamus. From the thala- 
mus the impulses are carried by the anterior stalk and ansae 
lenticularis et peduncularis to the somaesthetic area of the 
cortex. 

The lateral, or lower, fillet 27 forms an oblique ridge on 
the dorsum of the tegmentum. It trends upward and in- 
ward over the superior cerebellar peduncle to the posterior 
quadrigeminal body, where its fibers terminate. It rises 
chiefly from the ventral and dorsal parts of the cochlear 
nuclei (principally the opposite one) and ends in the posterior 
quadrigeminal body. It undergoes partial relay in the 
nucleus of the superior olive and of the trapezoid body on 
each side, and the nucleus of the lateral fillet on the same 
side, and it receives a small bundle of fibers from the antero- 
lateral ascending cerebellar tract. The greater number of 
its fibers cross through the trapezium; some are uncrossed. 
Thus the lateral fillet forms the second stage in the auditory 
conduction path. The auditory nerve constitutes the first 
stage, the lateral fillet the second stage, the posterior 
brachium the third and the aerustic radiations the fourth 

(27) Lemniscus lateralis. 



64 THE BRAIN AND SPINAL CORD. 

stage. The last stage ends in the cortex of the superior and 
the transverse temporal convolutions. 

(4) The Superior Peduncle 291 of the cerebellum continues 
upward from the dorsal surface of the pons. It forms a 
ridge near the median line of the mid-brain which ends in 
front at the inferior corpus quadrigeminum. The lower 
fillet winds inward over its anterior extremity. It is joined 
to its fellow by a sheet of white matter, the valve of Vieus- 
sens. 29 The fibers of the cerebellar peduncles bend ventrally 
beneath the corpora quadrigemina and then, for the most 
part, decussate, inferior to the iter, through the median 
raphe. These crossed fibers with the few uncrossed run for- 
ward toward the inferior surface of the optic thalamus, where 
they inclose the red nucleus, and help to form the stratum 
dorsale of the hypothalamic region (Forel). Many of the 
fibers terminate in the red nucleus and from it others rise 
and proceed forward to the thalamus. Though most of the 
superior cerebellar peduncle is centripetal and forms a seg- 
ment of an indirect sensory tract, it also contains efferent 
fibers which rise in the red nucleus. 

(5) The Olivary Fasciculus. — This is the bundle 30 
which takes form at the inferior olive where it probably 
rises. It runs through the formatio reticularis of medulla 
and pons up to the mid-brain. In the tegmentum it pierces 
the decussation of the superior cerebellar peduncles, running 
ventral to the longitudinal bundles; and then, bending lat- 
eralward. it ascends external to the posterior longitudinal 
bundle. It ends in the globus pallidus of the lenticular 
nucleus (Flechsig). Flechsig believes that the olivary 
bundle and the fasciculus triangularis of Helwig (in the 

(28) Brachium conjunctivum. 

(29) Velum medulare anterius. 

(30) Fasciculus tegrnenti centralis. 



MID-BRAIN. 65 

spinal cord) are parts of the same afferent conduction path. 
(6) The Crossed Descending Tract of the Red Nucleus. 
— Formed by axones from that nucleus, it immediately de- 
cussates with its fellow of the opposite side and descends, in 
the medial part of the lateral fillet, to the medulla ; it then 
mingles with the antero-lateral ascending cerebellar tract, 
in the medulla; and, in the cord, occupies the dorso-lateral 
part of the crossed pyramidal tract. It ends in the lateral 
horn and center of the gray crescent. It may be traced to 
the lumbar segments of the spinal cord. 



CHAPTER IV. 



THE GRAY AND WHITE MATTER OF THE CERE- 
BRUM AND MID-BRAIN. 

In the mid-brain, white matter is found in the crustas 
and tegmentum, separated by the gray substantia nigra; and 
on its dorsum are the corpora quadrigemina and internal 
geniculate bodies composed of gray matter. Gray matter 
forms nearly the whole of the inter-brain. The deep part of 
the hemispheres is white matter; a thin envelope of gray 
matter, the cortex, incloses it. Imbedded in that white mat- 
ter, is the basal ganglion of the hemisphere, called the corpus 
striatum. Both the gray and the white matter are richly 
supplied with blood vessels. 

The Neurone. — The essential element in the nervous sys- 
tem is the neurone. The neurone comprises the cell-body, 
its processes and end-organs. The cell-body, perikaryon, or 
neurone center, is a reticulated mass of protoplasm of varia- 
ble form, and ranges between ten microns and fifty microns 
in size. It is nucleated and may possess several nucleoli. 
Its shape which is spherical, fusiform, pyramidal, stellate or 
polygonal, is dependent upon the number and mode of origin 
of its processes. The processes of the neurone are from one 
to eight or a dozen in number and are of two kinds, namely, 
the dendrites and the axones. Dendrites, like the cell-body, 
are protoplasmic in composition and of irregular contour. 
They branch freely, ending either by multiple division in 
sharp filaments or in knobbed ends constituting special end- 



THE GRAY AND WHITE MATTER. 6? 

organs. They conduct toward the cell-body and are there- 
fore afferent, or sensory. Axones, or neuraxones, are smooth 
and fibrillar in character. They give off many side branches, 
called collaterals, and terminate by multiple division in an 
end-brush, which is in relation with another neurone or with 
a muscle fiber. In the latter case the fibers of the end- 
brush spread out into disc-like platelets, motorial end-plates, 
and underneath the sareolemmse apply themselves to the 
fibers of a muscle. Axones conduct from the neurone center. 
They are efferent, or motor. Both axones and dendrites are 
usually insulated by the white substance of Schwann, which 
forms their medullary sheaths. In all probability neurones 
differ in chemical constitution and in electric status, hence 
chemicals, electricity and diseases appear to exercise a se- 
lective power and affect certain neurones without influencing 
others (see note). 

In the brain and spinal-cord and in the optic nerves two 
forms of sustentacular tissue are found supporting the 
neurones. (1) Neuroglia, which is most abundant in gray 
matter. It is an epiblastic structure made up of richly 
branched nucleated cells whose processes form a fine reticu- 
lation in the larger meshes of the connective tissue network. 
(2) Connective tissue network. — That is of mesoblastic 
origin and is formed by branching processes from the inner 
surface of the pia mater. It transmits the blood-vessels into 
the nervous substance. The neurones constitute 53 per cent 
of the brain and cord (cell-bodies. 6 per cent) and the sus- 
tentacular tissue 47 per cenl (Donaldson). 

The white matter of the cerebro-spinal axis is made up 
chiefly of bundles of medullated axones imbedded in neurog- 
lia and supported by connective tissue. The fibers possess 
no neurolemma. 



68 THE BRAIN AND SPINAL CORD. 

The gray matter of the central nervous system is composed 
of cell-bodies and dendrites, chiefly, but also contains axones. 
These nerve elements are supported by connective tissue and 
blood vessels and are imbedded in a great abundance of 
neuroglia. The nerve fibers in the gray matter are to a large 
extent non-medullated. 



NOTE. 

In the first edition of, this work the name of the nerve ele- 
ment was spelled "neuron" according to Waldeyer. But the 
new spelling, already used by Profs. Barker and Gordinier 
in their excellent works, has been employed in the revised 
edition to avoid confusion. Shaefer uses neuron in the 
sense of axone and Wilder of Cornell makes it synonymous 
with cerebro-spinal axis. 

The neurone is a nervous entity and in the embryo is 
structurally independent of all other neurones. When fully 
developed in man perhaps a very small number of neurones 
are united together by concrescence or protoplasmic bridges, 
but their predominant relation is certainly that of contact, 
or synapsis. 

TYPES OF NEURONES. 

1. The first type has a long axone, which preserves its 
identity though it may give off many collaterals. Found in 
brain and spinal cord (Golgi, or Deiter). 

2. The second type has a short axone, breaking at once 
into branches of apparently equal importance, the dendrax- 
one. Found in cerebellum (Golgfs cells). 

3. The third type has two or more axones — diaxone, tri- 
axone, polyaxone — as in the first layer of the cerebral cor- 
tex (Cajal). 



THE GRAY AND WHITE MATTER. 69 

ORDERS OP NEURONES. 

1. The first order has distal process in relation with the 
periphery, as spinal-ganglion or anterior cornu neurones. 

2. The second order has cell-body or distal process in 
relation with neurone of first order. In like manner there 
are neurones of the third, fourth, fifth order, etc. 

FUNCTIONS OF NEURONES. 

1. Afferent. 2. Associative. 3. Efferent. 

QUALITIES PECULIAR TO DENDRITES: 

1. They may be absent or very numerous. 

2. They are protoplasmic in composition like the cell-body. 

3. In contour they are irregular, knobbed or gemmulated. 

Except in sensory spinal nerves (Cajal). 

4. End in sharp points, or in sensory neurones of first 

order, they may end in bulbous or spherical end- 
organs. 

5. Afferent in conduction: (1) sensory; (2) excito-re- 

flex; and (3) trophic (?). 

QUALITIES PECULIAR TO AXONES : 

1. Single or multiple (absent in latent neurones). 

2. Fibrillar in character. 

3. Smooth and regular in contour. 

4. Terminate in form of end- tufts which in motor neurones 

of the first order form motorial end-plates. 

5. Efferent in conduction: (1) motor; (2) inhibitory; 

(3) trophic (?) ; and (4) secretory (?). 
On section both dendrite and axone undergo Wallerian 
degeneration in the disconnected part. That part remain- 
ing in connection with the cell-body atrophies and degen- 
erates late, degeneration of Nissl. 



yO THE BRAIN AND SPINAL CORD. 

The gray matter of the cerebrum and mid-brain is con- 
veniently grouped into three classes: 

I. Cortical. 
II. Ganglionar. 
III. Central, or Ventricular. 

I. The Cortical Gray Matter. 
It consists of a thin envelope, the cortex (or bark), which 
forms the surface of the hemispheres and incloses the 
(white) medulla, the centrum semiovale. The cortex varies 
in thickness from a line to a quarter of an inch. Thickest 
on the surface of the convolution, it grows thinner to the 
bottom of the sulci. It is of a reddish, or yellowish, gray 
color depending on the richness of the blood supply. By long 
observation of lesions in the brain and by anatomical and 
physiological investigation the cortex has been mapped out 
into quite definite areas. Psychic function, probably, is de- 
pendent upon the associated activity of all parts of the 
brain; but common sensory and motor regions have been 
denned with considerable exactness. The latter are found in 
the equatorial zone of the hemisphere (Figure 1). That 
sensori-motor region is called the motor area (or Eolandic 
area) when referring to the efferent, or motor, tracts which 
rise in it; and, when reference is made to the sensory tracts 
which terminate in it, the sensori-motor region is called the 
somaesthetic area. Notice in Fig. 1 that the motor speech 
center and head area comprise the foot of the inferior frontal 
convolution and the lower two-fourths of the central gyri; 
the writing center of Gordinier and the upper extremity 
area occupy the foot of the middle frontal, a part of the 
superior frontal and the third fourth (numbered upward) 
of the central convolutions; and the trunk and lower ex- 



THE GRAY AND WHITE MATTER. J I 

tremity areas are contained in the upper one-fourth of the 

central convolutions and in the superior parietal gyrus. The 
head, shoulder, trunk and lower extremity are also repre- 
sented, and in this order, in the marginal gyrus, the para- 
central and quadrate lobules (see Fig. 2). In the same 
figure the centers of smell and taste may be observed in 
the uncus and hippocampal convolution and the visual cen- 
ter in the cuneus. The latter extends somewhat into the 
convex portion of the occipital lobe. Locate the remaining 
special centers on the convex surface (see Fig. 1). In the 
angular and occipital convolutions is the center for visual 
memories; in the supramarginal gyrus appears to be the 
center for motor memories; the sensory auditory center is 
seen in third and fourth-fifths of the superior and in the 
transverse temporal gyri, and the center of auditory memories 
is in the immediately adjacent cortex. The naming center 
is probably in the third temporal convolution. 

All the above motor, somaesthetic and special sense area- 
are provided with projection fibers which connect them with 
definite muscle groups and surface regions and with the or- 
gans of special sense. Other parts of the cerebral cortex- 
possess no projection fibers; they are believed to be associa- 
tive in function. Anterior association center. — According 
to Flechsig that part of the frontal cortex which is anterior 
to the motor and somaesthetic regions determines the tem- 
perament and individuality of the person ; while the posterior 
association center, composer! of those portions of cortex situ- 
ated between the sensory and motor regions of the equatorial 
zone, in front, and the visual cortex of the occipital lobe, 
behind, determine the intellectuality of the individual. To 
acquire knowledge of the external world is thus the function 
of the posterior association center. Flechsig regards the 



72 THE BRAIN AND SPINAL CORD. 

Island of Rett as the middle association center and lesions 
in it have been found associated with paraphasia. 

Destructive lesions of parts of the motor or sensory cortex 
cause merely loss of certain motions and sensations repre- 
sented by those parts, but ablation of association centers dis- 
connects the sensory, the memory and the motor regions (as 
in aphasia), causes change of temperament and impairment 
of the so-called moral and intellectual faculties. Ablation 
of the visual memory center or auditory memory center pro- 
duces mind-blindness in the former and in the latter mind- 
deafness. 

To the naked eye a fresh section of the cerebral cortex 
shows a stratified arrangement; sometimes three gray lam- 
inae can be made out which are separated by the inner and 
outer white lines of Bailarger; and, in the hippocampus 
major, a superficial (reticulated) white layer also is easily 
seen. A typical section of cortex, which is usually taken 
from the parietal lobe, presents under the microscope five 
layers, as follows: 

(1) The Superficial, Molecular, or Neurogliar Layer. — 
It is next the pia mater and is believed to be associative in 
function. Neuroglia forms the bulk of it, but it contains 

(a) a few irregular cell-bodies (Neurones of Cajal) possess- 
ing dendritic and from one to three axonic processes; and 

(b) a fine network composed of gray and medullated nerve 
fibers. These medullated fibers form the superficial white 
layer, above referred to, visible to the naked eye in the hip- 
pocampus major. The fibers in the neurogliar layer are for 
the most part dendrites of cell-bodies in adjacent lamina?. 
The nerones of the neurogliar layer probably eive rise to the 
short association fibers of the cerebral cortex. 

(2) The Second Layer is the layer of small pyramids. 



THE GRAY AND WHITE MATTER. 73 

The pyramids are closely ' packed together. They point to- 
ward the pia. Their dendrites run outward and ramify in 
the neurogliar layer; their bases, from which the axones 
issue, are directed toward the white core of the convolution. 
The axones, after piercing the deeper gray laminae, receive 
the white substance of Schwann and enter into the forma- 
tion of the medulla (the centrum semiovale) of the hemi- 
sphere. The small pyramids are believed to be chiefly sen- 
sory in function, but to a small extent are associative ac- 
cording to Cajal. 

(3) Third, the Layer of Large Pyramids. — The large 
pyramids have the same direction as the small ones. They 
are arranged in elongated groups separated by radiating 
fibers. The pyramids are largest in the Eolandic area, and 
the grouping is most distinct near the underlying fourth 
layer. The function of the large pyramids is chiefly motor 
(Dana), but it is also associative (Cajal). Their dendritic 
processes pass outward; their axones, as medullated fibers, 
run down into the white center and capsula interna. Seven 
or eight collaterals are given off from each axis-cylinder pro- 
cess before it becomes medullated, and these collateral? 
ramify in the adjacent gray matter, basal ganglia, etc. 

The third layer is as thick as the two overlying it ; it varies 
between one-fiftieth and one-twenty-fifth of an inch. Its 
formation is like that of the cornu Ammonis, the hippocam- 
pus major. 

(4) Fourth,, the polymorphous layer is a very thin one, 
about a hundredth of an inch in thickness. Tts cell-bocHes 
are small and irregular. Tboy pos^oss many dendrites ami 
one axone, or axis-cylinder process. A few of the latter, 
piercing the tbird and second layer? of gray substance, 
ramify in the first; the larger number of them proceed info 



74 THE BRAIN AND SPINAL CORD. 

the white center and comprise a great number of the long 
association fibers (Cajal). Probably a few of them become 
projection fibers. 

(5) Fifth. — This is the layer of fusiform cell-bodies. It 
has the formation of the claustrum, hence the synonym for 
the fifth layer, the claustral formation. It is placed next 
the white center. It is a thick layer, one twenty-fifth of an 
inch, and merges imperceptibly into the medulla beneath it. 
The cell-bodies in the main have their long axes perpendicu- 
lar to the surface of the hemisphere; but, beneath the 
fissures, they are parallel with it. In the convolutions they 
lie between the radiating fibers. Under the sulci they are 
parallel with the association fibers which join adjacent gyri. 
The long association fibers probably belong for the most part 
to the fusiform and polymorphous neurones (Cajal). 

To this typical cortex there are four principal exceptions, 
viz.: 

(a) On the medial surface of the occipital lobe near the 
calcarine fissure, there are six to eight layers produced by 
the division of the layer of large pyramids by a lamina of 
irregular cell-bodies, with or without the presence of the 
normal fourth layer. The latter may divide the fifth layer. 
There are very few large pyramids in this situation. 

(b) The gray cap of the olfactory lull has but four 
layers, namely: first, the nerve fiber layer composed of the 
non-medullated fibers of the olfactory nerves which join the 
bulb from below; second, the stratum glomerulosum, the 
glomeruli being made up of the synapses formed by the olfac- 
tory fibers and the dendrites of the mitral neurones; third, 
the layer of mitral cell-bodies, whose protoplasmic processes 
ramify in the second layer and whose axones pass into the 
medullary stem, after piercing the granular layer; and 



THE GRAY AND WHITE MATTER. 75 

fourth, the granular layer, which lies next the medullary 
stem and is composed of small irregular neurone-centers, like 
those in the rust-colored granular layer of the cerebellum. 
The last two (the third and fourth) are sometimes called the 
granular layer, thus reducing the number to three. The 
axis-cylinder processes of the mitral (or conical) neurones, 
medullated, form the olfactory tract. 

Destruction of the olfactory bulb, olfactory tract or olfac- 
tory area in the cortex causes almost exactly the same result, 
viz., anosmia in the same side of the nose. The olfactory 
path is, chiefly, if not entirely, uncrossed. 

(c) In the hippocampus major are five layers of cortical 
matter, which represent the first four of typical cortex. The 
first layer, the one bounding the dentate fissure, is' the invo- 
luted medullary lamina. This is the regular network of 
medullated fibers, but is more highly developed than in 
typical cortex. It is just beneath the pia, a little neuroglia 
only intervening. The second layer is composed of closely 
packed small cell-bodies (granules). It is the stratum 
granulosum. There are no neurone-centers in the third 
layer, but a dense network of pyramid. and granule dendrites. 
The first three layers represent the neuroglial' layer of typ- 
ical cortex. The fourth is a very thick layer and is made up 
of pyramids of medium size. To the fourth Layer the second 
and third layers in typical cortex correspond. The medul- 
lated axones of the pyramids constitute the thin lamina o( 
white matter called the alveus which forms (he ventricular 
surface of the hippocampus major. Fifth. — Between the 
alveus and the pyramids is a thin, polymorphous layer, which 
resembles the fourth layer of parietal cortex. 

(d) The fourth exception fco the typical cortex is found in 
the floor of the fissure of Sylvvus. It consists of a very great 



j6 THE BRAIN AND SPINAL CORD. 

thickening of the fusiform layer. All five laminae are 
present. This cortex resembles the claustrum. 

The claustrum (a rampart) is an isolated sheet of gray 
matter, in structure much like the fifth layer of the cortex. 
It is cortical matter according to Meynert. It is a vertical 
antero-posterior sheet placed medial to the island of Reil, 
and lateral to the external capsule. The surface in contact 
with the external capsule is. smooth, but the external surface 
is convoluted to coincide with the gyri insula}. At its lower 
border it joins the lenticular nucleus. It is made up of 
fusiform cell-bodies, which lie between the fibers of the 
uncinate fasciculus (see below — association fibers). 
II. Ganglionar Gray Matter. 

It is found in the great ganglia which have already been 
considered. They should be re-studied in this connection. 
They are as follows: 

1. In the hemisphere: 

Corpus striatum, composed of the caudate and the 
lenticular nucleus. 

2. In the inter-brain: 

The optic thalamus, the external geniculate body, 
nucleus Luysi and red nucleus. 

3. In the mid-brain: 

The internal geniculate body, the anterior and the 

posterior quadrigeminal body, a lateral half of the 

substantia nigra, and other less important nuclei 

in the tegmentum. 

The corpus striatum is an ovoid mass of reddish-gray 

matter containing pigmented multipolar cell-bodies of various 

sizes, those of large size being more numerous in the nucleus 

lenticularis than in the nucleus caudatus. The axones of 

those cell-bodies run both toward the pons and toward the 



THE GRAY AND WHITE MATTER. J J 

cerebral cortex. The corpus striatum, therefore, forms a 
way-station in an efferent conduction tract and, perhaps a 
less important one, in an afferent tract. 

Of the centrifugal fibers note the following three bundles: 
(a) A large bundle of axones from the striate body, the 
intermediate tract, runs down through the internal capsule 
and crusta to the nucleus pontis. It forms a thin inter- 
mediate zone between the pyramidal tract and substantia 
nigra in the mid-brain. Axones from the nucleus pontis 
continue the tract to the cerebellum (Flechsig). (b) Eding- 
er's bundle rises in the caudate nucleus and in the putamen 
of the lenticular nucleus and, running through the anterior 
segment of the internal capsule, terminates in the optic 
thalamus, chiefly; but also in the substantia nigra and 
posterior quadrigeminal body, (c) The centrifugal axones 
of the ansa lenticularis. They rise principally from the 
putamen of the lenticular nucleus. After running through 
the medullary laminae of that nucleus they proceed medial- 
ward beneath the globus pallidas. The greater number end 
in the nucleus of Luys ; certain others terminate in the optic 
thalamus and the remainder in the tuber cinereum and gray 
matter in the lateral wall of the third ventricle. 

The best known centripetal fibers received by the corpus 
striatum are (a) certain fibers of the medial fillet contained 
in the ansa lenticularis, and (b) the olivary bundle (Flech- 
sig). They arborize about the cell-bodies in the globus 
pallidus, whence other axones rise and continue to the 
somaesthetic area of the cerebral cortex. 

Lesions of the corpus striatum affecl the internal capsule 
and may cause, if extensive, hemiplegia and hemianesthesia 
of the opposite side of the body and partial deafness chiefly 



78 THE BRAIN AND SPINAL CORD. 

in the opposite ear and hemianopia of the corresponding 
halves of both retinae. 

The optic thalamus 1 is made up chiefly of gray matter 
containing multipolar and fusiform cell-bodies. The white 
matter, the internal medullary lamina, divides the gray into 
nuclei, of which Mssl has described about twenty. They 
may be grouped as follows: 

(1) The internal, or medial, nucleus is joined to the 
opposite inner nucleus by the gray (or middle) commissure 
and is continuous with the gray matter in the wall and floor 
of the third ventricle; but the internal medullary lamina 
separates it from the other nuclei of the same thalamus. 

(2) The external, or lateral, nucleus is the largest. It 
extends from dorsal to ventral surface the entire length of 
the thalamus (Burdach). It forms the terminal nucleus for 
the larger part of the tegmental fibers and the nucleus of 
origin for most of the fibers of the ansae peduncularis et 
lenticularis and anterior stalk of the thalamus. Destruction 
of this nucleus interrupts the common sensory path, and 
causes hemianesthesia of the opposite side. 

(3) The nucleus of the anterior tubercle, or anterior 
nucleus, receives the anterior pillar of the fornix and the 
bundle of Vicq d J Azyr. 

(4) The posterior nucleus is a small one. It is situated 
under the pulvinar between the geniculate bodies. 

(5) The nucleus of the pulvinar is an important one. It 
receives about twenty per cent of the optic fibers and gives 
rise to a corresponding number of the afferent fibers in the 
optic radiations to the occipital lobe, hence a lesion of the 
pulvinar impairs vision. 

(6) The nucleus of the habenula belongs to the epithala- 

(1) Thalamus. 



THE GRAY AND WHITE MATTER. 79 

mus. It lies beneath the trigonum habenulae. It receives 
fibers from the rhinencephalon through the pineal stria, also 
fibers from the optic tract, and originates a bundle of fibers, 
fasciculus retronexus (Meynert), which may be traced back 
through the tegmentum to the interpeduncular ganglion in 
the substantia nigra. 

(7) The central nucleus (center median of Luys) is 
situated deep in the thalamus below and between the internal 
and external nuclei and dorsal to the red nucleus. It gives 
origin to some fibers of the ansa lenticularis which run to 
the cortex. 

The white matter of the optic thalamus has, for the most 
part, an indefinite arrangement. Into it' enter the tegmental 
and fillet fibers and end, chiefly, in the lateral nucleus. It 
also receives axones or collaterals from every part of the 
cerebral cortex and sends fibers to the somaesthetic and spe- 
cial sense areas. The white matter forms the S-shaped 
internal medullary lamina and is continued in numerous 
bundles of fibers which enter the hemisphere. These bundles 
are as follows: 

(1) The anterior pillar of the fornix (having pierced the 
thalamus) and the bundle of Vieq d'Azyr 2 descend from the 
anterior nucleus through the inferior surface to the corpus 
albicans. 

(2) From the external surface two groups, which rise 
chiefly in the lateral nucleus, proceed into the cortex of the 
general sensory region (the somaesthetic area) : (a) The 
inferior is the ansa peduncularis. It passes below the len- 
ticular nucleus with the internal capsule, and enters into 
both the medullary laminn? of that nucleus and the external 
capsule. Tt ends chiefly in the cortex of the ascending 

(2) Fascicularis mamillaris. 



80 THE BRAIN AND SPINAL CORD. 

frontal and ascending parietal convolutions. Its fibers are 
medullated at the beginning of the ninth month (Flechsig). 
(b) The superior group is the ansa lenticularis, which 
pierces the superior lamina of the internal capsule and then 
the nucleus lenticularis, where some of its fibers are inter- 
rupted. It assists in forming the external capsule and ends 
in the central gyri, the paracentral lobule, the foot of the 
superior frontal convolution and the entire limbic lobe. The 
fibers of the ansa lenticularis become medullated at the end 
of the ninth month (Flechsig). 

(3) The anterior stalk streams from the anterior end of 
the lateral nucleus, via the frontal segment of the internal 
capsule, into the frontal lobe. The fibers of the stalk end in 
the cortex at the foot of the inferior and middle frontal 
gyri, the anterior half of the superior frontal convolution 
and the middle of the gyrus fornicatus. Its fibers receive 
their medullary sheaths near the end of the tenth month 
(Flechsig). From the same part of the cerebral cortex the 
frontal cefebro-corticopontal tract rises. 

The ansae peduncularis et lenticularis and the anterior 
stalk of the thalamus are called the cortical fillet; they 
carry ordinary sensations, chiefly from the fillet and superior 
cerebellar peduncles, up to the somaesthetic cortex. Inter- 
ruption of the cortical fillet stops all common sensory 
impulses. 

(4) A large pencil of fibers, the optic radiations? passes 
from the pulvinar and external geniculate body through 
internal capsule to the visual centers in the occipital lobe. A 
number of the optic radiations are efferent and end in the 
anterior quadrigeminal body. Destructive lesion of the optic 
radiations of either side produces hemianopia of the same side 
of both retinae. 

(3) Radiatio occipitothalamica. 



THE GRAY AND WHITE MATTER. 8l 

(5) Another pencil of fibers radiates from the region of 
the internal geniculate body through internal capsule to the 
auditory area in the temporal lobe. It constitutes the acustic 
radiations* If the acustic radiations be destroyed the result 
is partial deafness affecting chiefly the opposite ear. 

The red nucleus 5 of the tegmentum is situated beneath 
the optic thalamus. It is a way-station in the indirect 
sensory tract, receiving the opposite superior cerebellar pe- 
duncle and, by its axones, continuing the tract to the optic 
thalamus and somaesthetic cortex. It also receives efferent 
axones and gives origin to two bundles: (a) One centrifu- 
gal bundle of axones (the crossed descending tract), after 
crossing over in the tegmentum, descends, first, with the 
medial portion of the lateral fillet; second, through the lat- 
eral area of the medulla, and, third, through the dorso-lateral 
part of the crossed pyramidal tract in the spinal cord. 
Gradually diminishing, it disappears at the first lumbar 
segment. It ends in the lateral horn and center of the gray 
crescent of the spinal cord, (b) The red nucleus also sends 
a bundle of axones through the opposite superior peduncle 
of the cerebellum to the corpus dentatum. 

The nucleus hypothalamicus (Luysij is a pigmented bi- 
convex mass of gray matter placed ventro-lateral to the red 
nucleus, and between it and the fibers of the crusta. Tt 
constitutes an important relay for certain fibers of the medial 
fillet, Certain descending fibers from the striate body termi- 
nate in this nucleus. Tt is also joined io the lamina einerea 
and tuber cinereum by a bundle of fibers that accompanies 
Chidden 's commissmv along the medial pari of the optic 
tract. This bundle constihilcs Mevnertfs commissure. 



(4) Radiatlo temporothalamlcn. 

(5) Nucleus ruber. 



82 THE BRAIN AND SPINAL CORD. 

The external geniculate body? which receives eighty per 
cent of the optic fibers (Von Monokow) and forms a relay 
in the optic path, and the internal geniculate body, 1 which 
is a way-station in the auditory tract, have been sufficiently 
described. Ablation of the former interrupts the optic path 
and of the latter the auditory path. 

The anterior pair of the corpora quadrigemina 8 represent 
the corpora bigemina, the optic lobes, of birds, fishes and 
reptiles. They are composed of three laminae: (1) The 
superficial white matter, the stratum zonale. That layer 
with the fibers of the interior is continuous, through the 
anterior brachium, with the optic tract and radiations. Many 
of them are crossed fibers. (2) The stratum cinereum forms 
a cap of gray matter beneath the stratum zonale. In struc- 
ture it resembles the interior of the posterior bodies. (3) Its 
multipolar cell-bodies increase in size toward the second gray 
layer, the stratum opticum. In that, the cell-bodies are 
very large. They are grouped in masses between the abun- 
dant fibers from the outer root of the optic tract, which 
arborize about them. They give rise to axones which asso- 
ciate the optic fibers with the nuclei of the third, fourth and 
sixth cranial nerves, and with the cilio-spinal center in the 
cervical cord. The stratum opticum rests upon the quad- 
rigeminal lamina. Some gray matter is scattered through 
the latter, and Tartuferi calls it the "stratum lemnisci." The 
anterior quadrigeminal body forms a terminal nucleus for 
certain fibers of the superior lemniscus, which bring to it 
ordinary sensations from spinal and cranial nerves. 

A bundle of fibers (the anterior longitudinal bundle) rises 
from the anterior quadrigeminal body, and descends along 

(6) Corpus geniculatum laterale. 

(7) Corpus g-eniculatum mediale. 

(8) Colliculi anteriores corporum quadrigeminorum. 



THE GRAY AND WHITE MATTER. 83 

the ventral surface of the posterior longitudinal bundle to 
the anterior cornu of gray matter in the cervical part of the 
spinal cord. This bundle rises in relation with the optic 
fibers and ends in the cilio-spinal center, which gives origin 
to white rami communicantes. It is one segment of the 
reflex arc concerned in dilating the pupil. 

Destructive lesions affecting the anterior quadrigeminal 
bodies produce loss of reflex movement of the eye-balls, loss 
of pupilary reflex and loss of accommodation. 

In the posterior pair of the quadrigeminal bodies 9 the 
white fibers are continuous, behind, with the lateral fillet; 
and with the posterior brachium, antero-externally. The 
interior of the posterior bodies is gray matter. It con- 
tains a network of fine fibers, and small multipolar cell- 
bodies. The latter are in relation with the terminal end-tufts 
of the lateral (lower) fillet fibers, and give origin to the 
fibers of the posterior brachium. The posterior bodies are 
united beneath the sulcus longitudinalis both by decussating 
fibers of the fillet and by gray matter. In distinction from 
the anterior bodies, the posterior pair may be called the 
auditory lobes; they arc well marked only in those mammals 
having highly specialized organs of hearing, and form an 
important way-station in the auditory conduction path, hence 
their destruction causes the same symptoms as interruption 
of the acustic radiations, namely deafness affecting chiefly 
the opposite ear. 

Substantia Nigra.— The small pigmented multipolar cell- 
bodies which make up the substantia nigra form, first, a 
terminal nucleus for certain fillers of the medial filler and a 
nucleus of origin for other fibers which continue in that 
tract (Barker); and, second, a. terminal way-station for the 

(9) Colliculi posteriores corporum quadri.uvnmioruni. 



54 THE BRAIN AND SPINAL CORD. 

fasciculus retroflexus of Meynert and for ceitain fibers of 
Edinger's bundle from the corpus striatum. Beyond this 
terminal station the efferent tracts are probably continued, 
but they have not been traced. 

III. Central, or Ventricular, Gray Matter. 
It is located (1) in the floor and walls of the third 
ventricle, (2) in the middle commissure of that ventricle, 
and (3) around the Sylvian aqueduct. 

(1) The lamina cinerea and tuber cinereum form a sheet 
of gray substance that connects the inferior surfaces of the 
hemispheres and may be called their inferior (or great) gray 
commissure. From the floor of the third ventricle it extends 
laterally beneath the optic thalamus, and is continuous with 
the anterior perforated lamina. The gray matter of the floor 
extends up a short distance on the medial surface of the 
thalamus opticus; and in that upturned part is located the 
anterior end of the motor oculi nucleus. The inferior gray 
commissure receives efferent fibers through the ansa lenticu- 
laris from the corpus striatum, and is joined to the nucleus 
of Luys by the fibers of Meynert" s commissure. 

(2) The middle commissure 10 joins the internal nuclei of 
the optic thalami. It is continuous with this upward exten- 
sion of the gray floor of the third ventricle. In the middle 
commissure are cell-bodies and transverse fibers. The latter 
appear to be loops which reach only to the median line; at 
least many of the fibers do not cross to the opposite side. 

(3) The nuclei of the third (oculomotor) and of the 
fourth (trochlear) cranial nerves are found in the gray 
matter about the Sylvian aqueduct. In it also is a part of 
the motor nucleus of the trigeminal, or fifth, nerve. Lesions 
which involve the trochlear and oculomotor nuclei, as a rule, 

(10) Massa intermedia. 



THE GRAY AND WHITE MATTER. 85 

also involve the fibers of the tegmentum and the resnlt is 
ocular paralysis on the same side and impaired sensation 
(hemiataxia) on the opposite side of the body. 

The white matter of the cerebrum and mid-brain is com- 
posed of three definite systems of fibers : 

1. Projection, or peduncular, fibers. 

2. Transverse, or commissural, fibers. 

3. Association fibers. 

I. Projection" Fibers. 
They are composed first of the medullated axis-cylinders 
of the large and medium-sized pyramids and of a few of the 
polymorphous neurones in the cerebral cortex; and second, 
of medullated axones of neurones whose centers are situated 
in masses of gray matter below the cerebral cortex. The 
projection fibers are therefore both centrifugal and centripe- 
tal. They run through the mid-brain to the cerebral cortex 
and vice versa, connecting the cortex, directly or indirectly, 
with all parts of the body, throwing or projecting a picture 
of every part and organ upon the cerebral cortex. Many of 
the fibers are interrupted in the basal ganglia, especially of 
the centripetal fibers. Within the hemisphere the projection 
fibers help to form the centrum semiovale and the corona 
radiata and then, converging, form the internal capsule. 
More distally (hey arc divided into two great groups of 
fibers, the crusta and the tegmentum, separated by the 
substantia nigra. 

CENTRIFUGAL, OR MOTOR, PROJECTION FIBERS. 

The crustae comprise most of the centrifugal, or motor. 
fibers, namely, the intermediate bundle, the frontal cerebro- 
corticopontal tract, 11 the pyramidal tract and the temporal 

(11) Tractus cerebro-oorticopontalis frontalis. 



86 THE BRAIN AND SPINAL CORD. 

cerebro-corticopontal tract. 12 The intermediate tract extends 
from the corpus striatum through the deep part of the crusta 
to . motor cranial nuclei and to the nucleus pontis whose 
axones run- by way of the middle cerebellar peduncle to the 
cortex of the opposite hemisphere of the cerebellum. It thus 
forms a segment of an indirect (through the cerebellum) 
efferent, or motor path. The fronto-pontal tract rises from 
the feet of the second and third frontal gyri and the anterior 
half of the first frontal gyrus and from the middle of the 
gyrus f ornicatus. It traverses the centrum semiovale, corona 
radiata, anterior segment of the internal capsule and internal 
one-fifth of the crusta to the ventral area of the pons, where 
it terminates in the nucleus pontis (chiefly) and in the 
nuclei of motor cranial nerves (Flechsig). According to 
Dejerine, the temporo-pontal tract extends from the temporal 
lobe through the inferior lamina (and posterior part of the 
superior lamina) jof the internal capsule and outer one-fifth 
of the crusta to the same nucleus; but according to Spitzka 
some of its fibers end in nuclei of motor cranial nerves. Thus 
it should be noted that, with the exception of those fibers to 
motor nuclei of the cranial nerves, each of the three tracts 
above mentioned, — viz., the intermediate, fronto-pontal and 
temporo-pontal, — constitutes a segment of an indirect efferent 
path which is interrupted in the nucleus pontis and then 
continued by the axones of that nucleus through the middle 
peduncle of the cerebellum. 

Axones from the Rolandic cortex constitute the pyramidal 
tract. 13 Descending through the centrum semiovale, corona 
radiata, genu and anterior two-thirds of the posterior segment 
of the internal capsule, the pyramidal tract comprises the 

(12) T. cerebro-corticopontalis temporalis. 

(13) Fasciculus longitudinalis (pyramidalis) pontis. 



THE GRAY AND WHITE MATTER. 87 

middle three-fifths of the crusta, the ventral longitudinal 
fibers of the pons, the pyramid of the medulla and the crossed 
and uncrossed pyramidal tracts of the spinal cord. The 
fibers of the pyramidal tract, with a few exceptions, cross 
over to the opposite side; they end in the motor nuclei of 
cranial and spinal nerves. Fibers enter the nucleus of the 
trochlear (or fourth cranial) nerve on the same side and a 
few descend to the motor nuclei of other cranial "nerves and 
to the anterior cornu of gray matter in the spinal cord with- 
out decussation ; all other pyramidal fibers terminate on the 
side opposite to their origin. Cranial fibers. — Those fibers 
of the pyramidal tract which end in the nuclei of cranial 
nerves rise in the lower (two-fourths) and anterior part of 
the Rolandic, or motor area, including also that part of the 
marginal convolution situated above the genu of the corpus 
callosum. They run through the genu of the internal cap- 
sule and, chiefly, through the inner portion of the middle 
three-fifths of the crusta ; a considerable number run through 
the outer portion of the pyramidal area. They terminate in 
the motor nuclei of cranial nerves. Upper extremity fibers. — 
The fibers of the pyramidal tract that end in the cervical par; 
of the spinal cord, and through it innervate the muscle? of 
the upper extremity, take their origin from the fool of the 
middle frontal gyrus and the adjacent part (third-fourth) c c 
the central convolutions, the foot of the superior frontal 
gyrus and the adjoining part of the marginal gyrus nexl 
behind the head confer and directly above the anterior pari 
of the tmncus corporis eallosi. These fibers run through 
the posterior segment of the internal capsule just behind the 
genu, and through the crusta immediately external fo thr 
cranial fibers. Those fibers which innervate the muscles o* 
the thumb, fingers and hand, rise lowest down in the arm 



88 THE BRAIN AND SPINAL CORD. - 

area of the cortex and occupy the posterior part of the arm 
bundle in the internal capsule and the external part of it in 
the crusta. The fibers which control the shoulder muscles 
rise in the upper part of the cortical area and form the 
anterior and internal part of the arm bundle in the capsula 
interna and crusta, respectively, while the wrist, fore-arm, 
elbow and arm are innervated by means of fibers which are 
intermediate in both origin and course. Trunk fibers. — The 
trunk fibers of the pyramidal tract rise in the superior fourth 
of the ascending frontal gyrus and in the contiguous part 
of the marginal convolution immediately in front of the 
paracentral lobule. In the internal capsule the trunk fibers 
run just behind those to the fingers and just external to 
them in the crusta. Lower extremity fibers. — A large num- 
ber of the pyramidal fibers terminate in the lumbar enlarge- 
ment of the spinal cord and carry impulses to the nerves of 
the lower extremity. They originate in the upper fourth of 
the ascending parietal convolution, in the superior parietal 
gyrus and in the paracentral and quadrate lobules. The hip 
fibers rise farthest forward and the toe fibers farthest back- 
ward, immediately in front of the parietooccipital fissure. 
The fibers have the same relative position in the internal 
capsule ; in the crusta the hip fibers are internal and the toe 
fibers external. Fibers which innervate the muscles of the 
thigh, leg and small toes have this same relative position and 
order between the hip and great toe fibers both in their 
cortical origin and in their course through the internal 
capsule and crusta. 

Several bundles of centrifugal fibers are found in the 
tegmentum, namely, the anterior longitudinal bundle, the 
crossed descending tract of the red nucleus, a small part of 
the superior peduncle of the cerebellum, the descending root 



THE GRAY AND WHITE MATTER. 89 

of the trifacial nerve and certain fibers in the formatio reticu- 
laris. With these exceptions the tegmentum is centripetal, 
or sensory. 

Destruction by clot, tumor, or otherwise, of any of the 
above motor tracts causes (upper segment) paralysis of the 
particular muscles innervated through that tract. 

CENTRIPETAL, OR SENSORY, PROJECTION" FIBERS. 

The sensory fibers of the tegmentum comprise the olivary 
bundle, the fillets, the optic tract (outer root), and the 
greater part of the posterior longitudinal bundle and superior 
cerebellar peduncle; perhaps, also, certain fibers in the for- 
matio reticularis. Excepting a small number of fibers, all 
these bundles terminate in the basal ganglia; but the paths 
of conduction are continued through the internal capsule. 
In the capsula interna the centripetal projection fibers con- 
stitute the three systems of Flechsig (the cortical fillet) and 
the optic and acustic radiations. The former end in the 
somaesthetic area of the cerebral cortex, the latter terminate 
in the visual and auditory cortex. 

The exact origin of the three systems of Flechsig has not 
been determined, but they are known to rise, chiefly, in the 
lateral nucleus of the optic thalamus. The ansa peduncularis 
(first system of Flechsig) runs through the internal capsule 
behind the pyramidal tract in the inferior lamina. Some of 
its fibers enter the medullary laminae of the nucleus lenticu- 
Inris and others enter the external capsule; ultimately they 
all terminate in the central convolutions. The ansa lenticu- 
laris (second system of Flechsig) issues from the lateral 
surface of the thalamus higher np than the former loop and 
mingles with the pyramidal fibers in the internal capsule. A 
number of its fibers pierce ihc internal capsule (superior 
lamina) and are interrupted in the lenticular nucleus: they 



90 THE BRAIN AND SPINAL CORD. 

assist in forming the medullary lamina? of that nucleus and 
form a part of the external capsule. The lenticular loop 
terminates in the upper part of the central convolutions, the 
foot of the superior frontal gyrus, the paracentral lobule and 
the entire limbic lobe. From the anterior end of the optic 
thalamus streams a great pencil of fibers, called the anterior 
stalk (third system of Flechsig). It mingles to a small 
extent with the fibers of the pyramidal tract, but runs chiefly 
through the anterior segment of the internal capsule. The 
anterior stalk terminates in the feet of the inferior and 
middle frontal convolutions, in the anterior half of the su- 
perior frontal gyrus and in the middle of the gyrus f ornicatus. 
The three systems of Flechsig convey common sensory im- 
pulses to the somaesthetic area of the cerebral cortex. They 
are often called the cortical fillet. 

If the cortical fillet be severed, all common sensory 
impulses to that hemisphere are interrupted and complete 
loss of sensation on the opposite side of the body (hemiataxia) 
results. 

The acustic radiations and the posterior brachium continue 
the auditory path from the end of the lateral fillet, in the 
posterior quadrigeminal body, to the internal geniculate body 
and then, through the retrolenticular part of the internal 
capsule, to the transverse temporal gyri and the third and 
fourth fifths of the superior temporal convolution (Barker). 
Interruption of these fibers produces deafness in the opposite 
ear, which is not complete because the acustic path is not 
wholly crossed. 

The optic radiations rise in the external geniculate body 
and in the pulvinal of the optic thalamus. They continue 
the visual conduction path through the retrolenticular region 
of the internal capsule to the cortex of the cuneate lobe. 



THE GRAY AND WHI'lE MAT1ER. 91 

Half -blindness in the same side of both retinae results from 
section of the optic radiations. 

II. Commissural Fibers. 

They connect opposite sides of the cerebrum. They are 
contained in the corpus callosum and the anterior commis- 
sure', and in the commissura hippocampi. 

The corpus callosum is the great link between the hemi- 
spheres. Its fibers connect both similar and dissimilar parts 
of the cortices. It is made up of cortical axones, a few of 
them being projection fibers; and collaterals from the pro- 
jection fibers. All callosal fibers except the few peduncular 
fibers, end on the opposite side in arborizations about the 
cortical cells. 

The anterior commissure joins the opposite temporal and 
occipital lobes together (pars oceipito-temporalis) ; and the 
limbic lobes with each other and with the contra-lateral 
olfactory tract (pars olfactoria). 

The commissura hippocampi, the lyre, unites the hippo- 
campus major, the uncus and the optic thalamus with their 
fellows of the opposite side. 

III. Association Fibers. 

These fibers remain on the same side and connect parts of 
the same hemisphere. They are situated within or close to 
the cortex, the various parts of which they serve to unite. 
The short association fibers are probably the axones of the 
irregular cell-bodies (Cajal's) situated in the neuroglial- 
layer of the cortex. They unite contiguous parts of the same 
convolution and associate together adjacent convolutions, 
They comprise arcuate and tangential libers. They are the 
more numerous and very important. Among them are libers 
which connect the visual sensory area with the visual mem- 



92 THE BRAIN AND SPINAL CORD. 

cry area and the auditory sensory with the auditory memory 
area. Interruption of these association fibers gives rise to 
certain forms of sensory aphasia. 

The long association fibers are collected into bundles. The 
long association fibers rise chiefly from the polymorphous 
and fusiform layers of the cerebral cortex, but also, to some 
extent, from the pyramids in the second and third layers 
(Cajal). They are axones. Proceeding out of the lobe in 
which they rise, they arborize about neurones in more or less 
distant parts of the cortex. The long association fibers dip 
down into the centrum semiovale and bring into harmonious 
action the widely separated cerebral centers. Among the 
best known are the following bundles: 

(1) The cingulum, or the fillet of the gyrus fornicatus, is 
a bundle of fibers in the falciform gyrus (the fornicate and 
hippocampal gyrii), which almost entirely encircles the 
corpus callosum. It extends from the anterior perforated 
lamina, through the gyrus fornicatus and hippocampal con- 
volution, to the uncus. The fibers have been divided into 
three groups by Beevor, namely: (a) The anterior, which 
joins the anterior perforated lamina and internal olfactory 
root to the fore part of the frontal lobe, (b) The horizontal, 
which unites the frontal lobe and the gyrus fornicatus. And 
(c) the posterior fasciculus, which associates the lingual and 
fusiform gyri with the hippocampal gyrus and pole of the 
temporal lobe. 

(2) The Fornix.- — Each lateral half of the fornix 14 is a 
bundle of association fibers. Its anterior end (or pillar) is 
connected with the corpus albicans ; and, through the bundle 
of Vicq d'Azyr, also with the optic thalamus. The posterior 
pillar, descending in the middle horn of the lateral ventricle, 

(14) Corpus fornicis. 



THE GRAY AND WHITE MATTER. 93 

for the most part, disappears in the alveus of the hippo- 
campus major; but a small bundle of its fibers, constituting 
the corpus fimbriatum, continues to the uncus. 

(3) The Uncinate Fasciculus is a bundle, 15 with some 
sharply curved fibers, which arches over the main stem of the 
Sylvian fissure, and connects the uncus and the orbital part 
of the frontal lobe. It is situated near the basal surface. 
Its fibers spread out at both ends in the cortex, and they 
especially join the internal and posterior orbital and the 
third frontal convolution with the limbic lobe (Barker). 
Like the cingulum and fornix it is connected with the rhinen- 
cephalon. Lesion in any one of these three bundles causes 
disturbance of smell. 

(4) The Superior Longitudinal Fasciculus 1 ^ is a sagittal 
bundle located beneath the convex surface of the hemi- 
sphere, just above the horizontal ramus of the fissure of 
Sylvius. It joins the frontal cortex with the parietal and 
the external temporal. It thus associates the auditory and 
the visual memory centers with the motor speech center, 
hence aphasia is the result of its interruption. 

(5) The Inferior Longitudinal Fasciculus 11 is about on a 
level with the lateral ventricle. It passes near the outer wall 
of the descending and posterior cornua of that ventricle, and 
connects the temporal lobe to the occipital. In the temporal 
lobe its fibers cross at right angles those of the inferior lamina 
of the internal capsule. This fasciculus unites the auditory 
and visual memory centers, and thus associates the memories 
of things seen with the memories of things heard. 

(6) The Fasciculus Occipito-frontalis (Forel). — This is 
a large bundle of fibers formerly regarded as a part o( the 

(15) Fasciculus uncinatus. 

(16) Fasciculus longitudinalis superior. 

(17) Fasciculus longitudinalis inferior. 



94 THE BRAIN AND SPINAL CORD. 

corpus callosum. It is situated between the cingulum and 
the superior longitudinal bundle, just external to the lateral 
ventricle. It extends from the cortex of every part of the 
frontal lobe to the cortex of the convex surface and lateral 
border of the occipital lobe. Posteriorly, the fibers diverge 
to form a fan-like sheet, and that sheet enters into the ex- 
ternal boundary of the descending horn of the lateral ventricle 
and into the floor, lateral wall and roof of the posterior horn, 
hence the synonym, tapetum. Its particular function is 
unknown. 

(7) The Perpendicular Fasciculus. 19, — This is a very broad 
vertical bundle located just in front of the occipital lobe. 
Anteriorly, it extends from the inferior parietal convolution, 
above, down to the second and third temporal; and, poste- 
riorly, it joins the superior occipital convolution with the 
middle and inferior occipital and with the fusiform gyrus of 
the temporal lobe. Its function is doubtful. 

NOTE. 

The student will find many obscure points cleared up by 
a careful study of the embryology of the cerebrum (see 
Chap. XL). 

BLOOD SUPPLY OF THE CEREBRUM AND MID-BRAIN. 

The blood supply of the cerebrum and mid-brain is de- 
rived from the anterior choroid and the anterior and middle 
cerebral arteries, all branches of the internal carotid; and 
from the posterior cerebral arteries, which are terminal 
branches of the basilar artery. They form a remarkable 
anastamosis at the base of the brain, the circle of Willis. 19 
The circle of Willis (really a heptagon) extends from a 
point in the great longitudinal fissure, anterior to the 

(18) Fasciculus perpendicularis. (19) Circulus arteriosus. 



THE GRAY AND WHITE MATTER. 95 

optic commissure, back to the pons. It is about an inch, and 
a half long, and one inch in transverse diameter. In front 
are the anterior cerebral arteries converging forward from 
the internal carotids and uniting through the anterior com- 
municating artery. 20 The posterior communicating artery 21 
forms the lateral boundary of the circle. It forms the anas- 
tamosis between the internal carotid artery and the posterior 
cerebral. The posterior cerebral arteries bound the circle 
behind. The superior cerebellar arteries send several 
branches to the dorsum of the mid-brain. 

The large distal branches of the cerebral arteries are 
distributed chiefly to the cortex and medulla of the hemi- 
spheres; while the small proximal branches supply the 
ganglia and inter-brain. The former belong to the cortical 
system, the latter to the ganglionic system. 

CORTICAL SYSTEM. 

The anterior cerebral artery* 7 - enters the great lonsritudinal 
fissure. Winding around the genu of the corpus callosum, it 
runs back on the medial surface of the hemisphere to the 
parieto-occipital fissure. It has three branches: (1) An- 
terior internal frontal, which supplies the internal orbital 
convolution and olfactory bulb, the superior frontal and the 
anterior half of the middle frontal gvri. (2) Middle inter- 
nal frontal, is distributed to the corpus callosum. pyrus 
fomicatus, marginal convolution and upper end of the 
ascending frontal convolution. And (3) posterior internal 
frontal, which supplies the quadrate lobe and part of the 
superior parietal convolution. 

The middle cerebral, artery 2 * runs in the fissure of Svlvrue. 
It has four distal branches: (1) External and inferior 

(20) A. oomrrmnlonns anterior. (22) Artera cerebri anterior 

(21) A. rommiinlcars posterior. (23) Artera cerebri media. 



g6 THE BRAIN AND SPINAL CORD. 

frontal, to the anterior and posterior orbital and third fron- 
tal convolntions ; (2) Ascending frontal, and (3) Ascending 
parietal, to convolntions of the same name. The ascending 
frontal also supplies the foot of the middle frontal gyrus; 
and the ascending parietal arter}^ a part of both the superior 
and inferior parietal convolntions. And (4) Parietotem- 
poral, which supplies the supragmarginal and the angular 
and the superior and middle temporal gyri. 

The posterior cerebral artery?* winding from the basilar 
artery 25 outward around the mid-brain, breaks up into three 
cortical branches on the tentorial surface of the hemisphere. 
Their distribution is as follows: (1) Occipital, to the 
cuneus and the convex surface of the occipital lobe; (2) 
Uncinate, to the same convolution (hippocampal and lin- 
gual), and (3) Temporal (or tempero-sphenoidal), to the 
fourth, third and part of the second temporal gyri. 

These vessels of the cortical system and their many 
branches pierce the hemispheres perpendicular to the surface. 
They are distributed, the short, to the cortex, and the long, 
to the medulla of the hemispheres. To a limited extent they 
anastamose with one another, but they do not communicate 
with the ganglionic system. 

GANGLIONIC SYSTEM. 

Small arteries from the circle of Willis and from the 
cerebral arteries near the circle constitute this system. It 
is made up of six groups of vessels : 

(1) Antero-median Ganglionic. — They rise from the ante- 
rior cerebral arteries and anterior communicating. Piercing 
the lamina cinerea (and a few of them, the anterior perfo- 
rated lamina) they supply the bulb of the caudate nucleus 
and anterior wall of the third ventricle. 

(24) Artera cerebri posterior. (25) A. basilaris. 



THE GRAY AND WHITE MATTER. 97 

(2, 3) The -Antero-late vol .Ganglionic Arteries take their 
origin, on ^either side, from the middle cerebral artery, a little 
outside the circle of Willis. They pierce the anterior perfo- 
rated lamina and are distributed to the striate body, internal 
eapsnle and optic thalamus. One of this group is the len- 
ticulo-striate artery. It supplies almost the entire corpus 
striatum. On account of its frequent rupture, it is called 
the artery of cerebral hemorrhage (Charcot). 

(4) Postero-median Ganglionic. — These are branches of 
the posterior cerebral and posterior communicating arteries. 
They supply the inter-peduncular structures and crustas ; and 
(after piercing the posterior perforated lamina) the walls of 
the third ventricle and medial parts of the optic thalami. 

(5, 6) Poster o-lateral Ganglionic Arteries. — They rise, on 
either side, from the posterior cerebral artery after it has 
wound around the crusta. They are distributed to the pos- 
terior part of the optic thalamus, the geniculate bodies and 
corpora quadrigemina. 

The ganglionic arteries pass to their distribution without 
communicating with one another or with the cortical arteries. 
They are end-arteries of Cohnheim. Between the cortical 
and ganglionic systems, there is an area poorly supplied with 
blood. That is the area of cerebral softening. 

Choroid Arteries. 26 — They arc three in number. 

Anterior Choroid. — Coming from the infernal carotid ar- 
tery, the anterior choroid artery 27 enters the apex of the 
descending horn of the lateral ventricle; and supplies the 
inferior two-thirds of the choroid plexus, a part of the velum 
interpositum, the hippocampus major and corpus fimbria him. 

The Postero-latcral Choroid?* is a branch of the posterior 

(26) Arteries choroidere. 

(27) Arterta ohoroldoa anterior. 

(28) A. choroidea posterolateralis. 



g8 THE BRAIN AND SPINAL CORD. 

cerebral. It is distributed to the upper third of the choroid 

plexus of the lateral ventricle and to the velum interpositum. 

Poster o-medial Choroid. 29 — Also a branch of the posterior 
cerebral artery, it supplies the choroid plexuses of the third 
ventricle; and, with branches from the superior cerebellar, 
completes the supply of the velum interpositum. The pos- 
tero-lateral and postero-medial choroid vessels have their 
origin, course and distribution wholly within the great trans- 
verse and choroid fissures. 

Veins. 30 — The velum interpositum and lateral and third 
ventricles are drained by the common vein of G-alen. 31 The 
veins of Galen (vv. cerebri internee) are formed, one on either 
side, at the foramen of Monro, by the union of the veins of 
the striate body 32 and choroid vein. 33 

The Superior Cerebral Veins, 34 eight to twelve in number, 
carry away the blood from the superior surface of the hemi- 
sphere. They run obliquely upward and forward into the 
superior longitudinal sinus. 35 Just before emptying into the 
sinus they receive most of the medial veins. 36 

The Medial Cerebral Veins. — They drain the medial sur- 
face of the hemisphere. The veins of that surface which do 
not empty into the superior cerebral veins unite and form the 
inferior longitudinal sinus. 37 

The base of the cerebrum and border of its, convex surface 
are drained by the Inferior Cerebral Veins. 38 On the tentorial 

(29) Arteriae choroidea posteromedialis. 

(30) Vense. 

(31) V. cerebri magna. 

(32) V. corporis striati (sing.). 

(33) V. choroidea. 

(34) Vv. cerebri superiores. 

(35) Sinus sagitalis superior. 

(36) Vv. cerebri mediales. 

(37) Sinus longitudinalis inferior. 

(38) Vv. cerebri inferiores. 



THE GRAY AND WHITE JMATTER. 99 

surface of the hemisphere, these veins empty, against the 
current, into the lateral and superior petrosal sinuses. 39 
Those from the temporal and frontal lobes empty into the 
cavernous sinus. 40 In or near the fissure of Sylvius there 
are two inferior cerebral veins of large size. The middle 
cerebral vein, 41 which runs from the under surface of the 
temporal lobe, medialward, along the fissure of Sylvius to 
the cavernous sinus; and the great anastamotic vein of 
Trolard, whose course is much the same but in front of the 
Sylvian fissure. Eising on the parietal lobe, it winds inward 
along the lesser wing of the sphenoid bone to the anterior 
extremity of the cavernous sinus. The main trunks of all 
the cerebral vessels are contained in the pia mater. 

There are no lymphatic vessels in either the brain or spinal 
cord; perivascular lymph spaces carry the fluid from the 
interior to the subarachnoid spaces. 

(39) Sinus transversus and S. petrosus superior. 

(40) Sinus cavernosus. 

(41) Vena cerebri media. 



L.ofC. 



CHAPTER "V 



HIKD-BEAIN. 

Section I. The Cerebellum. 

The hind-brain is composed of the cerebellum and the pons. 
The cerebellum is the dorsal portion of the hind-brain. It is 
called the little brain. Its weight is about five ounces, 
slightly more than one-tenth of the whole brain. It is situ- 
ated in the posterior fossa of the skull, under the tentorium 
cerebelli and dorsal to the pons and medulla oblongata. 
Between it and the last two structures is inclosed the fourth 
ventricle. 1 

Function. — The cerebellum is an important way-station, 
or relay, in the indirect motor and indirect sensory paths. In 
response to impulses received from skin, muscles, tendons, 
joints and viscera, it is also believed to originate impulses 
which co-ordinate muscles and maintain equilibrium. More- 
over, according to Bussell, each cerebellar hemisphere exer- 
cises an important inhibitory function, through the superior 
peduncles, upon the opposite side of the cerebrum. Divi- 
sions. — The cerebellum is made up of two lateral parts, the 
hemispheres, 2 and a central part, uniting the hemispheres 
together, called the vermis cerebelli, or worm. 

The cerebellar hemispheres measure two inches from before 
backward and about the same in thickness, antero-internally ; 
but they taper rapidly toward the lateral borders. They are 

(1) Ventriculus quartus. (2) Hemisphaerium cerebelli. 



HIND-BRAIN. 101 

joined together by the worm, which forms the most elevated 
part of the cerebellum. 

The vermis, or worm, is a small elongated lobe, shorter 
and much thinner than the hemisphere. In animals lower 
than mammals, it is the only part of the cerebellum present. 
Its transverse ridges give it a worm-like appearance. It unites 
the upper half of the medial aspect of the hemispheres, their 
lower halves being separated by an anterior-posterior groove, 
called the valley, or vallecula. 3 The upper surface of the 
vermis is called the superior worm, or vermis superior; and 
the lower surface, the inferior worm, or vermis inferior. The 
superior and inferior surfaces are separated from one another 
at the posterior end of the worm by the great horizontal fis- 
sure; 4 anteriorly, the medullary stem 5 of the cerebellum 
separates them. At either end of the worm is a notch 
bounded by the vermis and the hemispheres, the anterior 
and posterior cerebellar notches. 

The posterior cerebellar notch, incisura cerebelli posterior, 
is occupied by the falx cerebelli. A prolongation of the 
medullary stem of the cerebellum issues from the incisura 
cerebelli anterior, or anterior cerebellar notch. 

The medullary stem splits, in its medial part, into two 
laminae: a superior, which forms the superior medullary 
velum and three pairs of peduncles, and an inferior, which is 
the inferior medullary velum. Separating at an acute angle, 
the two lamina? form the tent and lateral recesses of the 
fourth ventricle. 

The inferior medullary velum is the inferior lamina o( 
the medullary stem. It is a short plate of white matter, noi 

(3) Vallecula cerebelli. 

(4) Sulcus horizontalis cerebelli. 

(5) Corpus medullare. 

(6) Velum medullare posterius. 



102 THE BRAIN AND SPINAL CORD, 

more than a quarter of an inch long. It ends in a concave 
border from which a sheet of epithelium continues down over 
the fourth ventricle; and together they form the posterior 
half of the roof of that cavity. Laterally, the inferior velum 
extends to the flocculus of the hemisphere, and blends with 
the middle cerebellar peduncle. Of the worm it covers the 
nodulus, antero-superiorly. It bounds, dorsally, the lateral 
recesses of the fourth ventricle. 

The superior lamina of the medullary stem joins the cere- 
bellum immediately to the pons. The superior lamina is 
made up of three pairs of cerebellar peduncles and the supe- 
rior medullary velum. 7 They are the prolongations of the 
white matter which constitutes the corpus medullare of the 
cerebellum. 

The superior peduncles (crura ad cerebrum, or brachia 
conjunctiva) converge as they pass forward and upward to 
the posterior quadrigeminal bodies, where they disappear. 
They are joined to one another by a thin plate of white 
matter, the superior medullary velum, or valve of Vieussens; 
with the valve, they form the dorsal longitudinal fibers of 
the pons ; and, as such, the roof and lateral boundaries of the 
anterior half of the fourth ventricle. Beneath the corpora 
quadrigemina and aqueduct of Sylvius, most of the fibers of 
the superior cerebellar peduncles decussate, and pass into the 
hypothalmic region of the opposite side. They end chiefly 
in the red nucleus, which they surround. 

The inferior peduncles of the cerebellum (crura ad medul- 
lam) 8 issue from the cerebellum between the superior and 
middle peduncles. They first run ventrally to the dorsal 
surface of the pons, near the posterior border; and then, 
bending downward and backward (a flexion of more than 90 

(7) Velum medullare anterius. (8) Corpora restiformia. 



HIND-BRAIN. IO3 

degrees) , they converge in the posterior areas of the medulla 
toward the calamus scriptorius. They help to form the 
floor and to bound laterally the posterior half of the fourth 
ventricle. In the medulla they are called the restiform 
bodies. 

The middle peduncles (crura ad pontem) 9 join the cere- 
bellum to the lateral borders of the pons. They are con- 
tinuous with the ventral (or superficial) transverse and the 
middle transverse fibers of the pons. The middle peduncles 
are external to the superior and inferior peduncles, and are 
opposite the widest part of the fourth ventricle. 

Great Horizontal Fissure. — The cerebellum has one great 
fissure which divides it into upper and lower surface. The 
sulcus horizontalis cerebelli is shaped like a horse-shoe; its 
extremities are located on either side of the medullary stem. 
from which the fissure runs backward, dividing the border of 
each hemisphere and the posterior end of the worm. Tn the 
great horizontal fissure the remaining important fissures of 
the cerebellum terminate. They are nearly parallel with 
one another; hence, the cerebellum is laminated, not convo- 
luted like the cerebrum. The extremities of the greai 
horizontal fissure are separated from Hie fourth ventricle by 
a sheet of epithelium, on either side, uniting the borders of 
the superior and inferior medullary laminae, and bounding 
externally the lateral recesses. When the cerebellum is 
separated from the pons and medulla it presents along its 
anterior border between superior and inferior medullarv 
lamina? the transverse fissure. 

SUPERIOR SURFACE OE THE CEREBELLUM. 

The superior surface 10 of the cerebellum is bounded by the 
great horizontal fissure and Ihe superior lamina of the modul 
(9) Brachia pontls. (10) Facies superior. 



104 THE BRAIN AND SPINAL CORD. 

lary stem. It is divided into five continuous lobes by four 
crescentic fissures, called interlobular fissures. 11 

Fissures. — The interlobular fissures divide the worm and 
both hemispheres; and each lobe is composed of a central 
and two lateral portions, called lobules. These fissures are 
named in accordance with their relations to the lobules in the 
worm, viz. : 

(1) The Precentral Fissure, 12 which is located in the 
anterior cerebellar notch. It is between the lingula and 
lobulus centralis, in the worm; between the fraenulum and 
ala, in the hemisphere. 

(2) The Postcentral Fissure} 3 in the worm, separates the 
lobulus centralis from the culmen: and, in the hemisphere, 
the ala from the anterior crescentic lobule. The fissure fol- 
lows the anterior border of the superior surface. Both 
central fissures terminate on the dorsum of the superior 
medullary lamina. 

(3) PrecUval Fissure. — Behind the culmen and anterior 
crecentic lobules is the preclival fissure. It bounds the clivus 
and posterior crescentic lobules, in front. It ends at the 
junction of the anterior and middle thirds of the antero- 
lateral border in the great horizontal fissure. 

(4) The Post clival Fissure is located in the posterior 
cerebellar notch, from which it curves outward and forward 
in the superior surface of the hemispheres. It separates the 
clival lobe from the folium cacuminis. in the worm, and the 
postero-superior lobules in the hemispheres. It ends in the 
horizontal fissure at the junction of the posterior and middle 
thirds of the antero-lateral border. 

(11) Plssurae interlobulares. 

(12) Sulcus prsecentralis cerebelll. 
(IS) Sulcus postcentralis. 



HIND-BRAIN. 105 

Fissures and lobules of the upper surface of the cerebellum 
from before backward: 

Hemisphere. Worm. • Hemisphere. 

Fraenulum. Lingula. Fraenulum. 

Precentral fissure. 
Ala. Lobulus centralis. Ala. 

Postcentral fissure. 
Anterior crescentic. Culmen. Anterior crescentic. 

Preclival fissure. 
Posterior crescentic. Clivus. Posterior crescentic. 

Postclival fissure. 
Postero-superior. Folium cacuminis. Postero-superior. 
Great horizontal fissure. 

Lobes of Superior Surface. — These include the divisions 
of the worm and of the hemispheres, and are five in number. 

Lingula and Fraenula (Lobus lingulse). — The lingula 14 is 
a very small lobule of the vermis entirely concealed in the 
anterior cerebellar notch by the overhanging central lobule. 
It is a tongue-shaped group of four or five rudimentary 
transverse Laminae. It rests upon the superior medullary 
velum, with whieh its white center is continuous. Laterally, 
the lingula tapers off and is represented, if at all. in the 
hemisphere by a very thin folium called the fraenulum. 15 
The fraenulum is bounded by the superior cerebellar peduncle 
in front, and by the precentral fissure behind. The pre- 
central fissure separates the lobe el' the lingula from the 
central lobe. 

Central Lobule and Ma- (Lobus centralis). The lobulus 
centralis is situated between the precentral and postcentral 
fissures, in (he anterior cerebellar notch, h covers the lin- 
gula and in tun] is overhung by the culmen. Pout or five 

(14) Lingula cerebelli. (15) Vinculum lingua cerebelli. 



106 THE BRAIN AND SPINAL CORD. 

small transverse laminae make it up. On section, it is seen 
to form a single leaf of the medullary stem (arbor vitae). 
The laminae of the central lobule, continuing into either 
hemisphere, form a triangular or wing-like lobule, the ala 
(ala lobnli centralis). 

Culmen and Anterior Crescentic, Lobules (Lobns culmi- 
nis) . — In the culmen 16 the surface of the cerebellum reaches 
its highest elevation. It is a large lobule and occupies more 
than half of the upper surface of the worm. It is made up 
of three or four prominent laminae, which extend laterally 
into the hemispheres; and, there, form the anterior cres- 
centic lobules. 17 The latter occupy about one- third of the 
upper surface of the hemispheres. The preclival fissure 
separates the culmen and anterior crescentic lobules (the lobe 
of the culmen) from the clival lobe. 

Clivus and Posterior Crescentic Lobules (Lobus clivi). — 
The clivus 18 forms the posterior slope, as the culmen form? 
the summit, of the monticulus cerebelli. The clivus has 
about half the extent of the culmen. Its laminae are con- 
tinued into either hemisphere, where they form the large 
posterior crescentic lobule. 19 The increased size in the 
hemisphere is due to the expansion of the secondary folia 
found in the worm. The anterior and posterior crescentir 
lobules constitute the quadrate lobe. 20 which forms the 
anterior two-thirds of the superior surface of the hemi- 
sphere. The clivus and its hemispherical extensions are 
inclosed between the preclival and postclival fissures. 

The folium, cacuminis and postero-superior lobules (Lobus 
Caen-minis') lie behind the postclival and in front of the great 

lift) Culmen monticnll cerebelli. 

(17) Pars anterior lobuli quadrangularls. 

(18) Deelive monticuli cerebelli. 

(19) Pars posterior lobuli quadrangularis. 

(20) Lobus quadrangnlaris. 



HIND-BRAIN. 10/ 

horizontal fissure. The folium caeuminis 21 is the terminal 
lamina in the superior worm, and occupies the posterior 
cerebellar notch. It is beset with rudimentary folia, which 
are largely developed in the hemispheres. The postero- 
superior lobule 22 is, therefore, very large in comparison with 
the folium caeuminis. It expands lateralward to the postero- 
lateral border of the hemisphere, which it forms. It com- 
prises the posterior third of the hemisphere's superior surface. 

INFERIOR SURFACE OF THE CEREBELLUM. 

The inferior surface of the cerebellum 23 is prominent 
laterally and depressed centrally (as the organ is viewed 
inverted), the hemispheres being separated by the antero- 
posterior groove, called the vallecula. 24 The valley is occu- 
pied by the inferior worm and is bounded on either side by 
a small fissure, between the worm and the overhanging 
hemisphere, called the sulcus valleculas The inferior 
cerebellar surface is limited by the great horizontal fissure 
and the medullary stem of the cerebellum. It is more com- 
plex than the superior surface; and its fissures are more 
sharply curved forward as they pass from the worm into the 
hemispheres. 

Fissures of Lower Surface. — The interlobular fissure- of 
tin's surface are very dee]). They are three in number, 
namely: 

(1) The postnodular fissure is in the anterior end o\' the 
worm between the nodule and inula. In tin 1 hemisphere ii 
winds forward and outward between the inferior medullary 
velum and the tonsil, and then continues laterally between 

(21) Folium vermis. 

(L'Ln Lobulus semilunaris superior. 

(23) Fades cerebelli Inferior. 

(24) Vallecula cerebelli. 



1 08 



THE BRAIN AND SPINAL CORD. 



fiocculus and digastric lobule to the anterior end of the great 
horizontal fissure. 

(2) The prepyramidal fissure, between the uvula and 
pyramid, is very concave in the hemispheres. It curves out- 
ward and forward around the tonsil, separating it from the 
digastric lobule. It terminates behind the flocculus in the 
postnodular fissure. 

(3) The postpyramidal fissure, between the pyramid and 
tuber valvulse, is near the posterior end of the worm. It 
forms an oblique groove in either sulcus vallecula?, from 
which three concentric fissures extend into the hemispheres. 
The anterior of the three (the pregracile), usually consid- 
ered the postpyramidal fissure in the hemisphere, separates 
the digastric lobule from the postero-inferior lobule; the 
remaining two (midgracile and postgracile) subdivide the 
postero-inferior lobule into anterior and posterior slender 
and inferior semilunar sub-lobules. The last is bounded 
behind by the great horizontal fissure. 

Fissures and lobules of the lower surface of the cerebellum, 
from before backward: 



Hemisphere. 
Flocculus. 

Tonsil. 

Digastric lobule. 

Postero-inferior 
lobule. 



Worm. 
Nodule. 

Postnodular fissure. 
Uvula. 

Prepyramidal fissure. 
Pyramid. 

Postpyramidal fissure. 
Tuber valvulae. 



Hemisphere. 
Flocculus. 

Tonsil. 



Digastric lobule. 



Postero-inferior 
lobule. 



Great horizontal fissure. 
Lobules of Lower Surface. — They are not continuous with 
one another from the worm to the hemisphere as on the 



HIND-BRAIN. IO9 

upper surface. Excepting the posterior lobules, only a small 
ridge beneath the sulcus valleculas joins them together. The 
inferior lobes are four in number. Each is composed of a 
central and two lateral lobules. The lobule in the worm 
gives the name to the lobe. 

Nodulus and Flocculi (Lobus noduli). — The nodule 25 is 
a small lobule at the anterior end of the inferior worm. It 
is composed of three or four laminae, which project from the 
middle of the lower surface of the inferior medullary velum. 
It comprises a single branch of the arbor vitas. Though 
larger, it is the counterpart of the lingula on the superior 
velum. It is bounded by the sulcus valleculas on either side. 
The inferior medullary velum extends laterally from the 
nodule, and blends with the middle peduncle of the cere- 
bellum. In front of the tonsil, a fold of gray matter 
(peduncle of flocculus) 2,; appears on the velum. That gray 
matter enlarges more externally to a tufted mass, called the 
flocculus. The flocculus is separated from the tonsil and 
digastric lobule by the postnOdular fissure. The whole line 
of structures, namely, the nodule, velum, peduncle and floc- 
culus, form the lobe of the nodule'. 

Uvula and Tonsils (Lobus uvulae). — The uvula 27 com- 
prises a considerable part of the vermis inferior behind the 
nodule. It broadens backward and is widest next the pyra- 
mid. Rounded on either side by the sulcus valleculas, ii 
projects into. the valley like the uvula into the isthmus of 
fauces. Three moderate sized Laminae and six or eighi small 
folia make up the uvula. A slighl ridge, the furrowed band, 
joins it to the tonsil 28 in the hemisphere. Prom the furrowed 
band the tonsi] expands downward and backward forming a 
lobule of nearly a do/en sagittal laminae. The tonsil 

(25) Nodulus vermis. (27) Uvula vermis. 

(26) Peohinoulus flocculi. (28) Tonsilla cerebellt. 



110 THE BRAIN AND SPINAL CORD. 

amygdala) overhangs the side of the uvula and conceals the 
furrowed band, medially; and, behind, it conceals the con- 
necting ridge between the pyramid and digastric lobule. 
The fossa containing the tonsil is the bird's nest (nidus avis) . 
Behind the uvular lobe, composed of the above three lobules, 
are the prepyramidal fissure and the lobe of the pyramid. 

Pyramid and Digastric Lobules (Lobus pyramidis). — As 
seen from the surface, three or four distinct laminae make 
up the pyramid, 29 which is the most prominent lobule of the 
inferior worm. A low connecting ridge joins the pyramid 
to the digastric lobule in the hemisphere. The digastric 
(or biventral) lobule 30 is triangular in outline. Its base 
looks toward the flocculus and is bounded by the postnodular 
fissure; its apex is continuous with the connecting ridge. 
The laminae composing it radiate from the apex toward the 
base, and are divided into two groups by a very deep inter- 
lobular fissure. The postpyramidal fissure bounds it postero- 
externally, and separates it from the postero-inferior lobule. 

Tuber Valvule and Postero-inferior Lobules (Lobus tu- 
beris). — The tuber valvulae 31 forms the posterior end of the 
inferior worm. It resembles the lobules of the vermis supe- 
rior, because its half dozen tertiary laminae are continued 
into the hemispheres, the sulcus valleculas not cutting them 
off. The great horizontal fissure separates it from the folium 
cacuminis of the superior worm. The postero-inferior 
lobule 32 comprises the posterior two-thirds of the inferior 
surface of each hemisphere, extending from the digastric 
lobule to the postero-lateral border. Twelve to fifteen lam- 
inae compose the lobule. They are divided into three groups 

(29) Pyramis vermis. 

(30) Lobulus bi venter. 

(31) Tuber vermis. 

(32) Lobulus semilunaris inferior. 



HIND-BRAIN. Ill 

by the midgracile and postgracile fissures; the groups are 
named the anterior slender, or pregracile, posterior slender, 
or postgracile, and inferior semilunar. The inferior semi- 
lunar sublobule, only, is continuous with the laminae of the 
tuber. 

GRAY MATTER OF THE CEREBELLUM. 

The gray matter of the cerebellum is composed of cortex 
which covers the cerebellar laminae and of ganglia imbedded 
in the medullary center. 

1. Cortical Gray Matter. 

The cortex of the cerebellum (substantia corticalis) is 
made up of two microscopic layers, viz., (1) a superficial, 
molecular, or gray cellular layer, and (2) a deep, nuclear, or 
rust-colored granular layer. 

(1) Superficial, Molecular, or Gray Cellular Layer. — 
Thickest on the laminae and thinnest beneath the fissures, 
this layer contains small spheroidal, or stellate, cell-bodies 
with their processes, and large flask-like cell-bodies with their 
dendrites and axones (the cells of Purkinje) and a close 
network of fibers. 

Cells. — The bodies of PurkinjVs cells are located near the 
deep surface of the cellular layer (stratum gangliosum) . 
Each has one axone which, after piercing the granular layer, 
becomes a fiber of the medullary center (a projection fiber). 
From the outer end of each cell-body antler-like processes, 
the dendrites, are given off; they ramify toward the surface 
in a plane at righi angles to the intralobular fissures. The 
spheroidal cell-bodies form an outer and inner layer. The} 
have rich dendritic processes and one axis cylinder each. 
The dendrites ramify throughout the cellular layer. In the 
outer layer the stellate cell-bodies are smaller than in the 



112 THE BRAIN AND SPINAL CORD. 

inner layer. Their axis-cylinders run parallel with the sur- 
face and with the intralobular fissures. They branch freely 
and terminate in a manner unknown. The inner layer con- 
tains the "basket cells." Their axis-cylinder processes run 
parallel with the former, and give off vertical branches which 
descend to Purkinje's corpuscles and inclose them in a basket- 
work of filaments. 

Fibers of the gray cellular layers have three sources: (a) 
The dendritic and axonic processes of neurones within the 
layer; (b) The processes of cell-bodies in the granular layer. 
The latter comprise, first, the neurogiiar fibers of Bergmann 
(vertical), which extend from the glia cell-bodies in the 
granular layer outward to the surface of the lamina, where 
they form beneath the pia mater a f eltwork like the limiting 
membranes of the retinas; and, second, the axones of the 
cell-bodies in the granular layer, whose T-branches form 
horizontal fibers in the superficial layer, (c) The fibers of 
the medullary center (projection fibers) rise or end largely 
in the cellular layer. The axones of PurkinjVs neurones 
compose most of the centrifugal projection fibers. The cen- 
tripetal fibers, which rise either in other parts of the brain 
or in the spinal cord and ganglia, terminate in end-tufts or 
moss-like appendages (Cajal) chiefly in the superficial layer. 

(2) The deep, nuclear, or rust-colored granular layer is 
of uniform thickness. It blends centrally with the medullary 
stem. 

Cells of the Granular Layer. — The granules are small, 
round, or stellate cell-bodies, closely packed externally, but 
scattered among the projection fibers centrally. Each gran- 
ule has one axone. It runs out into the cellular layer, 
branches T-like, and forms many of the horizontal fibers of 
that layer. Dendritic processes are abundant. They ramify 



HIND-BRAIN. I I 3 

chiefly within the granular layer. The neuroglial' cell- 
bodies, which originate the vertical fibers of Bergmann, lie 
near the cells of Purkinje. 

Among the fibers of the granular layer are included the 
processes of the granules and glia cell-bodies, and the 
projection fibers. 

The functions of the stellate cells, the <f basket cells" and 
the granule cells are probably receptive and associate; they 
receive impulses through the centripetal projection fibers and 
transfer those impulses to the dendrites or bodies of Pur- 
kinje's cells. Purkinje's cells originate impulses for the 
coordination of muscular action (Gordinier), and for the 
inhibition of nervous activity in the opposite cerebral hemi- 
sphere (Russell). Hence lesions in the cerebellum produce 
incoordination, irritability and, rarely, convulsions. 
II. Ganglionar Gray Matter. 

The ganglia of the cerebellum are the corpus dentatum 
and the three nuclei of Stilling. 

The corpus dentatum 1 is a wavy, sinuous pouch of yellow- 
ish-brown gray matter imbedded in the medullary stem of 
each hemisphere. It is filled with white fibers, which i^suo 
from its anterior, open end 2 and form the greater part of the 
superior cerebellar peduncle. Stellate cell-bodies (from fi 
microns to 40 microns in diameter) are the essential element 
of both the corpus dentatum and Stilliug's nuclei. 

Nuclei of Stilling'. — One of these, a elulvphaperl mass, the 
cork-like nucleus emboliformis, partly closes the hilus of the 
dentate body. Medial to that is an elongated antero-posterior 
ganglion, bulbous behind, called the nucleus (jlobosms. The 
third nucleus is in the anterior end of the worm, Just above 
the fastigium of the fourth ventricle. It is called the 

(1) Nucleus dentatus. (2) Hlhis nude! drntaH. 



114 THE BRAIN AND SPINAL CORD. 

nucleus of the highest point of the roof, nucleus fastigii. In 

the two last the stellate cell-bodies are larger than in the 
nucleus emboliformis or corpus dentatum; but, otherwise, 
they are alike in structure. The nucleus fastigii and nucleus 
globosus form the terminal station for the acustico-cerebellar 
tract, which tract sends collaterals to the nucleus emboli- 
formis and corpus dentatum. In this manner these nuclei 
are associated with the vestibular nuclei (auditory) of the 
opposite side. 

WHITE MATTER OF THE CEREBELLUM. 

The white matter of the cerebellum is arranged in three 
systems similar to that of the cerebrum : 

I. Projection, or peduncular, fibers. 
II. Commisural fibers. 
III. Association fibers. 

I. Projection Fibers. 

These include all fibers of the medullary stem 3 as it issues 
from the anterior cerebellar notch. They are in continuity 
with the branches of the medullary stem 4 and together con- 
stitute the arbor vitse. Dividing medially into a superior 
and an inferior lamina (united laterally), the medullary 
stem forms the tent 5 and lateral recesses 6 of the fourth 
ventricle. The inferior lamina is the inferior medullary 
velum, 7 whose fibers pass into the nodule and flocculi. The 
superior lamina forms the superior medullary velum and 
three pairs of cerebellar peduncles. 

Superior Peduncles. — Two bundles of filters make up the 

(3) Corpus medullare. 

(4) Laminae medullares. 

(5) Fastfgium. 

(6) Recessus lateralis ventriculi quarti. 

(7) Velum medullare posterius. 



HIND-BRAIN. I I 5 

superior peduncles. 8 They are afferent and efferent. First, 
the fibers to the cerebrum which are axones of cell-bodies 
situated chiefly in the corpus dentatum, but which are 
joined by a few axones of PurkinjVs cells. This group of 
fibers ends chiefly in the opposite red nucleus, where the 
second group rises. The second group, rising in the opposite 
red nucleus, ends in the corpus dentatum. The greater 
number of fibers in the superior peduncles decussate in the 
tegmentum. The superior medullary velum 9 arches over the 
fourth ventricle between the superior peduncles. It is com- 
posed chiefly of longitudinal fibers running between the worm 
and the cerebrum. One distinct bundle, derived from the 
spinal cord, passes through it to the worm. It is the antero- 
lateral ascending cerebellar tract (Hoche). The decussating 
root-fibers of the fourth nerve (trochlear) course transversely 
through the superior velum, also certain commissural fibers 
of the hind-brain. 

Middle Peduncles. — They pass to the pons and form its 
ventral and middle transverse fibers. They also are both 
afferent and efferent. The fibers of the middle peduncle 10 
rise first from every part of the cerebellar cortex. They 
cross one another in the peduncle, fibers from the anterior 
part of the hemisphere running to the posterior portion of 
the pons, and vice versa. Passing toward the modi an line, 
the fibers end in the nuclei pontis and nuclei of tin 1 formatio 
reticularis on both sides of the raphe. Second, the remain- 
ing fibers are axones of cell-bodies situated mainly in the 
opposite nucleus pontis. The latter form a segment in the 
indirect motor paths contained, above the pons, in the medial 
and lateral fifths of the erusta. Collaterals from both groups 

(8) Brachia conjunctiva. 

(9) Velum medullar? antcrius. 

(10) Brachium pontis. 



I l6 THE BRAIN AND SPINAL CORD. 

of fibers ascend and descend in the pons. They run upward 
with both crustaB, but chiefly with the opposite one; and 
they accompany the fillet and posterior longitudinal bundle 
of the same side to the nuclei of the third, fourth and sixth 
cranial nerves. 

The Inferior Peduncles can be traced to the upper part of 
the hemispheres and to the worm. Inferiorly, they become 
the restiform bodies 11 of the medulla oblongata. The 
bundles of component fibers are very numerous: (1) The 
direct cerebellar tract, whose origin is in Clark's column of 
the cord and termination in the superior worm. (2) The 
external arciform fibers of the medulla (posterior and ante- 
rior), which rise in the nucleus gracilis and nucleus cuneatus 
and end in the vermis superior, the former on the same and 
the latter on the opposite side. (3) The acustico-cerebellar 
tract from the nuclei of the vestibular nerve to the opposite 
nucleus fastigii and nucleus giobosus. (4) A bundle from 
the lateral nucleus of the medulla to the cerebellar cortex on 
the same side. (5) The anterolateral, descending cerebellar 
tract, which runs from the cortex of the cerebellum to the 
anterior gray horn in the cord. (6) The internal arciform 
fibers to the opposite lower olive, the cerebello-olivary tract. 

Most of the fibers which leave the cerebellum by way of the 
middle and inferior peduncles are axones of PurkimjVs cells; 
they connect the cerebellum with the motor nuclei of cranial 
and spinal nerves. 

II. Commissural Fibers. 

The cerebellar hemispheres are joined by transverse fibers, 
of which there are two sets, namely : One near the anterior 
end of the worm beneath the central lobe, and the other at 
the posterior end of the worm. 

(11) Corpus restiforme (sing.). 



HlND-BRAlN t 117 

III. Association Fibers. 
Antero-posterior fibers join the cerebellar laminae to one 
another. They arch beneath the fissures, and remain in one 
hemisphere. 

BLOOD SUPPLY OF CEREBELLUM. 

Three pairs of arteries supply the cerebellum. The supe- 
rior cerebellar, from the basilar, supplies all the superior 
surface except a narrow zone at the posterior border; and 
the anterior inferior cerebellar, also from the basilar, and the 
posterior inferior cerebellar, from the vertebral, supply the 
inferior surface and the posterior part of the superior surface. 

The superior cerebellar artery, rising from the basilar just 
behind the posterior cerebral, from which it is separated by 
the oculomotor nerve, winds dorsally around the mid-brain 
and distributes branches to the geniculate bodies, corpora 
quadrigemina, velum interpositum and dorsal surface of the 
pons, besides the vermis superior cerebelli and nearly all the 
superior surface of the hemisphere. It anastamoses with 
both the inferior cerebellar arteries. The anterior inferior 
cerebellar is given off by the basilar near its origin. It runs 
lateralward, behind the flocculus, keeping close to the anterior 
border of the hemisphere. In its course it passes anterior to 
the abducent nerve and posterior to the facial and auditory 
nerves. The posterior inferior cerebellar artery is the largest 
branch of the vertebral and is given off just before the 
vertebral arteries unite and form the basilar. Passing first 
between the root-bundles of the hypoglossal nerve and then 
between those of the spinal accessory and vagus nerves, the 
posterior inferior cerebellar artery bends at a right angle 
backward and runs between the medulla and the cerebellar 
hemisphere where it divides into an internal and an external 



Il8 THE BRAIN AND SPINAL CORD. 

branch. The Internal branch follows the sulcus vallecula 
and gives branches to the medial part of the hemisphere and 
the vermis inferior. It anastamoses with its fellow of the 
opposite side. The External branch runs lateralward from 
the posterior cerebellar notch over the inferior surface of the 
hemisphere; its terminal branches wind around the postero- 
lateral border and communicate with the superior cerebellar 
artery on the upper surface of the hemisphere. The un- 
divided trunk of the posterior inferior cerebellar artery gives 
small branches to the medulla oblongata and supplies the 
choroid tela of the fourth ventricle. 

Three sets of veins carry the blood away. The superior 
cerebellar veins pour their blood against the current into the 
straight sinus. The inferior cerebellar veins empty in like 
manner into the lateral sinus ; and the lateral cerebellar veins, 
into the superior petrosal sinus. 

The trunks of both veins and arteries ramify in the pia 
mater. 

Lymphatics. — There are no lymphatic vessels in the cere- 
bellum, but the perivascular lymph spaces carry out the 
lymph and pour it chiefly into the subarachnoid space. 

Section II. The Pons Varolii. 

The pons is the ventral part of the hind-brain, the cere- 
bellum being its dorsal portion. The pons is developed from 
the floor of the epencephalon. It is so named because it 
forms the connecting link, or bridge, between the mid-brain, 
above, and the cerebellum and medulla oblongata, below; 
between the medulla and cerebellum, and between the two 
cerebellar hemispheres. 

In shape the pons is roughly cylindrical. A coronal section 
of it resembles an inverted transverse section of the penis. 



HIND-BRAIN. I ig 

It has a broad basal or ventral part 12 and a narrow dorsal 
portion. 13 

Size. — The pons is about one inch long. It is a little 
broader than long, and measures an inch, dorso-ventrally. 

Position. — It rests in the anterior end of the groove which 
extends from the foramen magnum to the dorsum sella?, 
and lies between and ventral to the hemispheres of the cere- 
bellum. Superiorly, it joins the mid-brain; and, behind, it 
is continuous with the medulla oblongata. 

Surfaces of the Pons.— The pons has four surfaces, viz., 
superior (attached) ; inferior (attached) ; ventral (free), 
and dorsal (free) ;■ and two borders, namely, right and left 
lateral, continuous with the middle peduncles of the 
cerebellum. 14 

The superior and inferior surfaces are made by section, 
and are directly continuous with the mid-brain above and 
the medulla below. 

Ventral Surface (Tuber annulare). — The ventral surface 
of the pons looks downward and forward, and rests on the 
sphenoid bone behind the sella Turcica. It is divided into 
lateral halves by the sulcus basilaris, containing the basilar 
artery. Antero-posteriorly, the surface is slightly convex. 
and is markedly so from side to side. It shows transverse 
striations, which converge laterally, due to the fibers thai 
form it and enter the middle peduncles of the cerebellum. 
The fibers of the tuber annulare are not exactly transverse in 
direction. Those at the anterior end of the pons are arched 
convex forward, and form a rounded margin, which covers 
the lower part of the crnsta^ of the mid-brain ; at the poste 
rior extremity of the pons, the fibers are convex backward 

(12) Pars basilaris pontls. (10 Rrachla pontls. 

(13) Pars dorsalls pontls. 



120 THE BRAIN AND SPINAL CORD. 

and partially conceal the pyramids of the medulla oblongata. 
The two roots of the 5th nerve (trifacial) 15 issue from the 
lateral border (Henle) of this surface, a little in front of the 
middle. 

The Dorsal Surface of the pons is concealed by the cere- 
bellum. Medial Portion. — It presents a median longitudinal 
elevation due chiefly to the superior peduncles of the cere- 
bellum 16 and valve of Vieussens. 17 The peduncles converge 
forward and upward and run beneath the posterior quadri- 
geminal bodies of the mid-brain. The valve spans the interval 
between the peduncles and forms the floor of the slight 
groove which separates them. A low and narrow ridge runs 
from the corpora quadrigemina down the middle of the valve. 
It is called the frenulum. In the superior medullary velum 
(or valve of Vieussens), the 4th cranial nerve (n. trochlearis) 
decussates and issues from its lateral portion on each side of 
the frenulum. 

Lateral Portion. — Each lateral portion of the dorsal surface 
is depressed. On this depressed portion, the lateral fillet 18 
produces a low ridge which, trending upward and toward the 
median line, winds over the anterior end of the superior 
peduncle and terminates at the posterior corpus quadri- 
geminum. This ridge is joined by a much slighter one, which 
runs from the valve outward and forward over the posterior 
end of the superior peduncle; it is caused by a bundle of 
fibers from the antero -lateral ascending cerebellar tract. 

WHITE MATTER OF THE PONS. 

The pons is composed of transverse and longitudinal white 
fibers and of gray matter. The transverse fibers are found in 

(15) Nervus trigeminus. (17) Velum medullare anterius. 

(1(5) Brachia conjunctiva. (18) Lemniscus lateralis. 



HIND-BRAIN. 121 

the ventral portion 19 of the pons; the longitudinal, in the 
dorsal part, 20 and also intersecting the middle transverse 
fibers. 

TRANSVERSE FIBERS OF PONS. 

The transverse fibers form three consecutive layers in the 
ventral area of the pons, viz., the ventral, the middle, and 
the dorsal layer. They lie one upon another. 

The ventral transverse fibers (superficial transverse) 21 
form a thin layer constituting the tuber annulare, or ventral 
surface of the pons. 

Middle Transverse Fibers (ventral deep-transverse). — 
These form a thick lamina dorsal to the ventral transverse 
fibers and in contact with the ventral lamina. They are 
intermingled with longitudinal fibers running from the 
cnistae (middle three-fifths) down to the pyramids of the 
medulla oblongata and with fibers of the fronto-pontal and 
temporo-pontal tracts which end in the pons. In the meshes 
between the intersecting fibers are masses of gray matter 
called the nuclei pontis. The middle and ventral transverse 
fibers form the middle cerebellar peduncles. 22 They are 
made up (1) of axones of Purkinje's cells which end in the 
nuclei pontis and nuclei of the formatio reticularis on both 
sides of the pons, and (2) of axones of cell-bodies in these 
same nuclei, especially the nuclei pontis, which terminate in 
the cerebellar cortex of the opposite side. 

The dorsal transverse fibers (dorsal deep transverse) com- 
pose a thin layer on the dorsum of the middle transverse and 
pyramidal fibers, separating thorn from the formatio reticu- 
laris. The dorsal transverse lamina is besl marked in the 
posterior part of the pons, where it is called the trapezium. 

(19) Pars basilaris pontis. (21) Fibrre pontis Superflclales. 

(20) Pars dorsalis pontis. (22) Brachia pontis. 



122 THE BRAIN AND SPINAL CORD. 

The trapezium forms the boundary between the dorsal and 
ventral areas of the pons. It rises chiefly from the nuclei of 
the cochlear nerve and, after decussating in the raphe, is 
continued up in the lateral fillet to the corpus quadrigeminum 
posterius. A few fibers join the tract directly from the 
cochlear nerve. The nuclei of the trapezium, superior olive 
and lateral fillet form way-stations for a number of its fibers. 
The trapezium and lateral fillet form the second stage in the 
auditory conduction path, the auditory impulses having 
reached the trapezium and lateral fillet through the auditory 
nerve are continued (a) through the brachium posterius and 
(b) the acustic radiations to the temporal cortex. 

LONGITUDINAL FIBERS OF PONS. 

Like the transverse, the longitudinal fibers of the pons are 
arranged in three distinct lamina?, viz.. the ventral, the middle 
and the dorsal. The last two are in contact with one an- 
other in the dorsal area 23 of the pons : but the ventral lamina 
is separated from the middle by the trapezium. 

The Ventral Longitudinal Fibers (ventral deep-longitu- 
dinal) are the pyramidal fibers. 24 They run from the middle 
three-fifths of each crusta down through the middle trans- 
verse layer of the pons to the pyramids of the medulla 
oblongata. They form a thick bundle on either side of the 
median line, which presses down the ventral transverse fibers 
and produces the sulcus basilaris. The ventral longitudinal 
fibers are to a small extent made up of fibers, probably col- 
laterals, from the middle cerebellar peduncles (chiefly from 
the opposite one) which run both toward the cerebrum and 
the spinal cord. The nuclei pontis, one on either side, are 
situated among them. The pyramidal tracts diminish in 

(23) Pars dorsalls pontis. 

(24) Fasciculi lon^itudinales pontis (pyramidales). 



HIND-BRAIN. 123 

size during their descent,^ because of the fibers which leave 
them to decussate and end in the nuclei of motor cranial 
nerves. 

Middle Longitudinal Fibers (dorsal deep-longitudinal). — 
These are contained in the formatio reticularis. They are 
dorsal to the trapezium, and lie in the floor of the fourth 
ventricle. Laterally, the middle lamina is in contact with 
the dorsal longitudinal layer, the superior peduncles of the 
cerebellum lying directly on it; but, medially, the two 
laminae are separated from one another by the fourth ven- 
tricle. The middle longitudinal fibers are mingled with 
many oblique fibers ; and, thus, there is produced the net-like 
arrangement suggesting the name, formatio reticularis. The 
formatio reticularis of the pons is continued in the medulla 
oblongata. Considerable gray matter is found in the meshes, 
especially in the part next the fourth ventricle. The latter 
contains the nuclei of the fifth, sixth and seventh cranial 
nerves and a part of the nucleus of the eighth nerve. The 
remaining gray matter constitutes the nuclei of the formatio 
reticularis, etc. In the formatio reticularis are contained six 
distinct bundles of longitudinal fibers : the fillet, the ante- 
rior and the posterior longitudinal bundle, the olivary bundle, 
the crossed descending tract from the red nucleus, and in the 
lower part of the pons the ascending root of the trifacial 
nerve. According to Hoche, also, the antero-latera] ascend- 
ing cerebellar tract. 

(1) The Fillet™ Fibers form a broad lint bundle next the 
trapezium. The width of the bundle is almost equal to half 
the transverse axis of the pons: the lateral Rllei lies just 
beneath the dorsal surface, and the medial runs along the 
raphe. Anterior to the pons we have the medial, superior 

(25) Lemniscus— L. Lateralis, L. Medialis. L. Superior. 



124 THE BRAIN AND SPINAL CORD. 

and lateral fillets, which have been traced through the teg- 
mentum of the mid-brain to the optic thalamus and the 
anterior and posterior quadrigeminal bodies. 

(2) Posterior Longitudinal Bundle. 26 — It is a small fas- 
ciculus situated near the raphe, and just beneath the giay 
matter in the floor of the fourth ventricle. It is con- 
tinued down into the anterior column of the spinal cord 
without decussation. Both ascending and descending fibers 
are found in it. Its longest ascending fibers rise in the 
anterior cornu of gray matter in the spinal cord. Fibers are 
added to it from the sensory nuclei of cranial nerves, and 
from the cerebellum by way of the middle peduncles. Along 
its course fibers leave it and end in the motor nuclei of 
cranial nerves, especially the third and fourth. The bundle 
ends in the hypothalmic region. Many of its fibers decussate 
through the raphe in the medulla pons and mid-brain; the 
remainder cross through the posterior commissure. Motor 
fibers run through the posterior longitudinal bundle from the 
nucleus of the sixth to the third nerve and from the motor 
oculi to the facial nerve. 

(3) The Anterior Longitudinal Bundle 27 descends from 
the anterior quadrigeminal body ventral to the posterior 
longitudinal fasciculus, through the mid-brain, pons and 
medulla; and, in the cord, it runs along the apex of the 
anterior cornu of gray matter in which it terminates in the 
cervical region. It is the pupillo-dilator tract. 

(4) The Olivary Bundle 28 is an ascending tract. It be- 
gins at the dorsal surface of the inferior olive from which it 
probably rises. It ascends through the formatio reticularis 
of the medulla, pons and mid-brain, and, according to 

(26) Fasciculus longitudinalis medialis. 

(27) Fasciculus ventralis. 

(28) Fasciculus tegmenti centralis. 



HIND-BRAIN. 125 

Flechsig, ends in the globus pallidus of the lenticular nucleus, 
though certain fibers may continue through the lenticular 
loop, without interruption, to the cortex. The olivary bundle 
is probably the second stage in the afferent tract of which the 
triangular tract of Helwig is the first stage. In the posterior 
part of the pons, the olivary bundle lies on the lateral part of 
the trapezium, between it and the fillet. Higher up it is in 
the center of the formatio reticularis, hence its synonym, 
central tegmental tract. 

(5) Crossed Descending Tract of the Bed Nucleus. — It is 
found in the pons among the medial fibers of the lateral 
fillet. It runs from the red nucleus through the raphe, in 
the upper part of the mid-brain; and, from there, descends 
to the lumbar region of the spinal cord (Barker). Its fibers 
gradually disappear in the lateral horn and center of the 
crescent of gray matter (see Mid-Brain). 

(6) Ascending Root of the Trifacial or Fifth Nerve (in- 
ferior sensory root) . 29 — In the lower half of the pons is seen 
a small bundle of fibers which begins near the tubercle of 
Rolando in the medulla oblongata. It runs forward close to 
the lateral part of the floor of the fourth ventricle and joins 
the superior sensory root ventral to the superior cerebellar 
peduncle. 

The dorsal longitudinal fibers (superficial longitudinal) 
form the medial portion of the dorsal surface of the pons. 
They bound laterally and form the roof of the anterior half 
of the fourth ventricle. The dorsal longitudinal fibers com- 
pose the supeiior peduncles of the cerebellum and the valve 
of Vieussens. The peduncles rest on the formatio reticu- 
laris. Between them the valve arches over the fourth ven- 
tricle (see Cerebellum). 

(29) Tractus spinalis nervi trigemini. 



126 THE BRAIN AND SPINAL CORD. 

GRAY MATTER OF THE PONS. 

In the pons gray matter is found in two situations: (1) 
in the interstices between the middle transverse and ventral 
longitudinal fibers, the nuclei pontis; and (2) in the for- 
matio reticularis, the floor of the fourth ventricle. 

The nuclei pontis are masses of gray matter, on either side 
the raphe, containing the bodies of multipolar nerve cells. 
They receive many fibers from the middle peduncles of the 
cerebellum and each contributes many to the opposite pe- 
duncle. The nucleus pontis of each side receives the 
terminals of the descending tracts which form the inner and 
outer fifths of the crusta and the intermediate bundle of the 
same, and thus connects these tracts with the cerebellum. 

The gray matter of the formatio reticularis includes the 
superior olive; the nuclei of the trapezium; the nuclei of 
the formatio reticularis; and the nuclei of the fifth, sixth 
and seventh cranial nerves, and a part of the dorsal nucleus 
of the auditory nerve. The nerve nuclei will be further 
noticed in the description of the fourth ventricle. 

Superior Olivary Nucleus? — It is situated in the lateral 
part of the formatio reticularis in the dorsal portion of the 
trapezium. It contains small bodied nerve cells; and, in 
this respect, resembles the olive of the medulla. In size it 
is microscopic. The superior olive constitutes a subordinate 
relay in the auditory path, receiving fibers from the cochlear 
nuclei of both sides and contributing fibers to both lateral 
fillets. In their course to the fillets, fibers of the auditory 
path form the trapezium. 

Nuclei of the Formatio Reticularis. — These nuclei are 
scattered in the reticular formation from the medulla to the 
anterior quadrigeminal bodies. They contain the bodies of 

(SO) Nucleus olivaris superior. 



HIND-BRAIN. \2*] 

large multipolar cells, hence the name adopted by Koelliker, 
Nucleus magnocellularis diffusus. The nuclei are interposed 
in the frequently interrupted tracts of the reticular forma- 
tion. Their neurones, which are both ascending and de- 
scending in conduction, send their axones toward the raphe, 
where they cross to the opposite side. Axones of Purkinje's 
cells and collaterals from the nuclei of cranial nerves 
terminate in relation with them. 

Lesions in the pons are usually attended by crossed paraly- 
sis. The paralysis and anesthesia of parts supplied by 
spinal and by bulbar cranial nerves are on the opposite side, 
but the fifth, sixth and seventh cranial nerves of the same 
side as the lesion are ajjt to be involved. Conjugate deviation 
occurs when the nucleus of the sixth nerve is affected; and 
strabismus when the root fibers, but not the nucleus, are 
involved. The strabismus is external if the lesion be irrita- 
tive and internal if the root fibers are destroyed. Destructive 
lesion in the nucleus of the seventh nerve causes inferior 
paralysis of the face, the frontalis, pyramidalis nasi, corru- 
gator supercilii and orbicularis palpebrarum not being 
affected. Complete facial paralysis occurs if the root-fibers 
of the facial nerve be destroyed in the genu or beyond it. 

BLOOD SUPPLY OF PONS. 

The vertebral, basilar, posterior cerebral and superior 
cerebellar arteries supply the pons. The short and transverse 
branches of the basilar artery furnish the greater portion of 
blood to the ventral area of the pons, while the superior 
cerebellar artery supplies the valve of Vieussens 81 and the 
superior cerebellar peduncles. 32 The branches enter the 
median raphe, also the substance of the pon* elsewhere, es- 
pecially along the nerve roots, and run at right angles to the 
surface into it. 

(31) Velum medullare anterius. 

(32) Brachia conjunctiva. 



CHAPTEE VI. 



THE AFTER-BRAIN, OR MEDULLA OBLONGATA. 

Situation. — The medulla oblongata is the distal, or caudal, 
part of the brain. It may be regarded as the expanded 
intracranial portion of the spinal cord, hence the synonym, 
spinal bulb. It occupies the basilar groove of the occipital 
bone, posterior to the pons; and is continuous with the spinal 
cord through the foramen magnum. Dorsally, it is in part 
concealed in the valley of the cerebellum. The vertebral 
arteries wind forward around it, and form the basilar at its 
junction with the pons. 

Size. — The medulla is about an inch long, and dorso- 
ventrally, is a half -inch thick. Its width at the lower end is 
a half-inch, also. At the upper extremity it measures from 
three-quarters of an inch to one inch in width. 

Its shape resembles an inverted frustum of a cone flattened 
dorso-ventrally at the base. The truncated apex of the 
frustum, which is nearly circular in outline, is continuous 
with the spinal cord; and the flattened base joins the pons 
Variolii. On the ventral surface, a transverse groove marks 
the boundary between the medulla and pons. The medulla 
oblongata is a bilateral organ composed of symmetrical 
halves. In the interior, the two halves are united by both 
gray and white matter in the raphe, but on the surface they 
are partially separated by the anterior and the posterior 
median fissure. 1 These fissures are continuations of the 

(1) Fissura mediana anterior, posterior. 



THE AFTER-BRAIN. I2g 

same in the spinal cord, but neither extends the whole length 
of the mednlla. The anterior median fissure is interrupted 
in the lower part of the mednlla by the crossing of two large 
tracts of fibers, forming the decussation of the pyramids ; 
while only through the lower half of the mednlla does the 
posterior median fissure extend. 

Origin.-^The medulla oblongata is developed from the 
metencephalon (mycencephalon) of the embryo. The met- 
encephalic floor and walls thicken and form the greater part 
of the medulla. Inferiorly, the roof undergoes some thick- 
ening; but it stretches out into a single layer of epithelium, 
superiorly, which is continuous at its upper end with the 
inferior medullary velum of the cerebellum. 

Ventricle. — The common cavity of the fourth and fifth 
brain vesicles persists in the mature brain as the fourth 
ventricle. The fourth is, therefore, the ventricle of the adult 
hind-brain and after-brain. 

SURFACES. 

The Medulla Oblongata presents four surfaces: the ventral, 
dorsal and two lateral, separated by the ventro-lateral and 
dorso-lateral grooves. In the npper medulla, the snrfncos 
are clearly defined; but they become less distinct -as they 
descend to the posterior and nearly circular extremity. 

The Ventro-lateral Groove 2 separates the ventral from the 
lateral surface, and is in line with the exits of the anterior 
roots of the spinal nerves. "N"o corresponding groove exists 
in the cord. From the ventro-lateral groove issue the roofs 
of the hypoglossal nerve. The abducens (or sixth) nerve 
rises in line with it from tho transverse groove between the 
pons and the mednlla. 

Dorso-lateral Groove. — The postero-lateral fissure of the 

(2> Sulcus iHterlalls anterior. 



130 THE BRAIN AND SPINAL CORD. 

spinal cord, continued into the medulla, becomes the dorso- 
lateral groove. 3 Through the fissure in the cord, pass the 
posterior roots of the spinal nerves; from the groove in the 
medulla, rise the accessory root of the eleventh and the roots 
of the tenth and ninth cranial nerves. The seventh and • 
eighth cranial nerves rise together at the anterior end of the 
groove. The last two come out between the medulla and 
pons. The dorso-lateral groove is not parallel with the axis 
of the medulla, but bends outward and forward as it ascends. 
Inferiorly, it is obliterated for a short distance by the crossing: 
of the direct cerebellar tract from the lateral to the posterior 
surface. This groove separates the lateral from the dorsal 
surface. 

The Ventral Surface 4 of the medulla, bounded on either 
side by the ventro-lateral groove, extends from the transverse 
sulcus behind the pons down to the spinal cord. It is made 
up of symmetrical halves united, below, bv the decussation of 
the crossed pyramidal tracts; but separated, above, by the 
anterior median fissure, which terminates at the posterior 
end of the pons in a blind foramen (foramen cecum of Yicq 
d'Azyr). On either side of the median fissure, the ventral 
surface presents a fusiform eminence, most prominent near 
the pons, called the pyramid. Two tracts of longitudinal 
fibers form the pyramid, viz. : the crossed pyramidal tract, 
next the anterior median fissure; and the uncrossed (direct) 
pyramidal tract, which runs next the ventro-lateral groove. 
Transverse fibers are also seen crossing the pyramid from 
within outward. A small bundle runs near the pons, called 
the ponticulus of Arnold ; and a more or less continuous 
sheet of fibers, the anterior external arciform fibers, emerges 
from the anterior median fissure apd winds around the me- 

(3) Sulcus laterlalls posterior. (4) Fades anterior. 



THE AFTER-BRAIN. I 3 1 

dulla to the dorsal surface, where its fibers enter the restiform 
body. 

The ventral surface is identical with the surface of the two 
anterior areas of the medulla. 

Lateral Surface. — There are a right and a left lateral 
surface. 5 Each is bounded by the ventro-lateral and the 
dorso-lateral grooves; and is inclosed between the roots of 
the hypoglossal nerve, ventrally, and those of the ninth, tenth 
and the accessory portion of the eleventh, dorsally. Lateral 
surface is synonymous with surface of the lateral area. The 
lateral surface is formed above by the olivary body; 6 below, 
by the lateral tract; and winding backward over both, the 
anterior external arciform fibers. 

The Olivary Body is an elongated eminence, a half-inch in 
length, situated just behind the pons. It is produced by the 
olivary nucleus in the lateral area of the medulla; and, 
superficially, is composed of fibers from the antero-lateral 
ground bundle of the lateral tract. 

Lateral Tract. 1 — It is made up of three great bundles of 
fibers: the antero-lateral ground bundle, 8 which, splitting 
into a superficial and a deep lamina, incloses the olivary 
nucleus; the antero-lateral descending cerebellar tract, 9 run- 
ning down the ventro-lateral groove; and the antero-lateral 
ascending cerebellar tract, 9 which runs up the dorso-lateral 
groove. At the junction of the medulla with the spinal cord 
the direct cerebellar tract passes from the lateral to the dorsal 
surface. The anterior external arciform fibers/ running 

(5) Facies laterialis. 

(6) Oliva. 

(7) Funiculus lateralis. 

(8) Fasciculus proprius antero-lateralis. 

(9) Fasciculus antero-lateralis superflclalis (descendens ami ns- 
cendens). 

(10) Fibra? arcuat;r externa? 



132 THE BRAIN AND SPINAL CORD. 

from the ventral surface backward to the restiform body, may 
be so numerous as to conceal the lateral tract and lower part 
of the olive. 

The dorsal surface of the medulla 11 comprises all the 
surface inclosed between the diverging dorso-lateral grooves. 
it embraces the surfaces of the two posterior areas of the 
medulla. 

Inferiorly, it is divided into lateral halves by the posterior 
median fissure/ 2 and presents four bundles of fibers in each 
half. From the fissure outward they are as follows: the 
fasciculus gracilis, fasciculus cuneatus, fasciculus of Rolando, 
and the direct cerebellar tract. 

The fasciculus gracilis is a continuation of the postero- 
median column of the spinal cord, and the fasciculus cunea- 
tus and fasciculus of Eolando are in direct continuity with 
the postero-lateral column of the cord. These three bundles 
leave the surface and end in the gracile, cuneate and Rolandic 
nuclei of the medulla. The direct cerebellar tract is con- 
tinued up from the lateral column of the spinal cord. 
Remaining on the surface, it runs up to the cerebellum 
through the restiform body. 

Superiorly, the dorsal surface, on either side, is formed by 
a large rounded band of fibers, the restiform body. 13 Of the 
superficial fibers in the medulla, the direct cerebellar tract, 
the antero-lateral descending cerebellar tract and the anterior 
and posterior external arciform fibers are continued into the 
restiform body; and, as we have already learned, the resti- 
form body contains, in addition to the above three tracts, the 
acustico-cerebellar tract, the tract from the lateral nucleus 
and the cerebello-olivary tract. It is also called the inferior 
peduncle of the cerebellum. A single layer of flattened epi- 

(11) Facies posterior. (13) Corpus restiforme. 

(12) Fissura mediana posterior. 



THE AFTER-BRAIN. I 33 

thelial cells stretches between the two restiform bodies, and 
roofs over the posterior part of the fourth ventricle. It is the 
roof epithelium. By it the dorsal surface is completed. 

The roof epithelium, seen in the mid-dorsal surface of the 
medulla., is of triangular shape; its base is attached to the 
inferior medullary velum of the cerebellum ; its apex, which 
is directed downward, covers the inferior angle of the fourth 
ventricle; and, laterally, it is attached to the clava, the 
cuneate tubercle and the restiform body. The line of attach- 
ment to the restiform body runs, first, obliquely upward and 
outward ; and then, transversely outward, inferior to the 
lateral recess. The borders of the epithelium become thick- 
ened by the addition of neuroglia, and are in continuity with 
the ependyma of the ventricle. The thickened apex of the 
epithelial lamina is called the obex. With the pia mater 
investing it, the roof epithelium forms the posterior choroid 
tela, 14 which is perforated in the median line near its apex 
by a foramen, the foramen of Magendie, 15 and over each 
lateral recess by the foramen of Key and Retzius. 10 These 
foramina establish communication between the subarachnoid 
space and the ventricle. On either side of the median line, a 
longitudinal invagination of the epithelial lamina dips into 
the ventricle and is occupied by a vascular fold of pia mater. 
The latter constitutes the choroid plexus 17 of the fourth 
ventricle. If the root' epithelium be torn away, as it usually 
is with the pia, a rough line of separation is seen winding 
over the restiform body. That line is the liguln. Two Layers 
of ependyma form it. 

INTERIOR OF THE MEDULLA. 

The medulla is made up of white and gray matter, which 
together bound the posterior part of the fourth ventricle. 

(14) Tela choroidea ventriculi quarti. 

(15) Apertura mediana ventriculi quarti. 

(16) Aperturaa laterales ventriculi quarti. 

(17) Plexus choroideus ventriculi quarti. 



134 THE BRAIN AND SPINAL CORD. 

WHITE MATTER. 

For the most part the white matter of the medulla is 
continuous with the longitudinal fibers of the pons and spinal 
cord, above and below, respectively; and with the inferior 
peduncles of the cerebellum, dorso-laterally. To these add 
the bulbar roots of the eighth to the twelfth cranial nerves to 
complete the list. 

Formatio Reticularis. — Superficially, the white matter is 
collected into great bundles of fibers, such as the pyramids, 
lateral tracts and restiform body; but, in the deep parts of 
the medulla, the white matter enters into a great network 
called the formatio reticularis, which has gray matter in its 
meshes and embraces all the medulla between the ventricular 
gray matter, dorsally, and the pyramid, olivary nucleus, and 
restiform body, ventro-laterally. The formatio reticularis 
contains many scattered fibers, processes of its intrinsic neu- 
rones, which form a frequently interrupted and, for the most 
part, a crossed ascending and descending tract. It is 
continuous, above, with the reticular formation of the pons, 
and, below, with the ground bundles of the spinal cord. It 
contains several distinct fasciculi of longitudinal fibers of 
which the following are the best understood: the posterior 
and anterior longitudinal bundles and the descending crossed 
tract of the red nucleus, which run throughout the medulla 
and are continued in the cord ; and, in the upper part of the 
medulla, the medial and superior fillets, the olivary bundle 
and the inferior, or spinal, root of the fifth cranial nerve. 
Transverse and oblique fibers are, likewise, numerous in the 
reticular formation. They are the internal arciform fibers. 
In the formatio reticularis is much gray matter which may 
be considered as the disintegrated H-shaped column continued 
up from the spinal cord. 



THE AFTER-BRAIN. I 35 

Raphe. — Fibers form only a part of the raphe which unites 
the lateral halves of the medulla. The raphe is, primarily, 
a sagittal lamina of neuroglia containing the bodies of nerve- 
cells and decussating, dorso-ventral and longitudinal' fibers, 
(a) The decussating fibers are chiefly the internal arciform. 
A few are commissural fibers between the nuclei of the pos- 
terior five cranial nerves, (b) Issuing from the anterior 
median fissure, the dorso-ventral fibers become the anterior 
external arciform fibers. Traced dorsally, some of them are 
found continuous with the acustic stria? in the floor of the 
fourth ventricle, while the greater number rise from the 
opposite nuclei gracilis et cuneatus. (c) The origin and 
destination of the longitudinal fibers are unknown. 

The white matter of the medulla is divided by the direction 
of its fibers into three classes or systems: (1) Transverse 
fibers; (2) Dorso-ventral fibers; and (3) Longitudinal 
fibers. 

(1) The Transverse Fibers of the medulla are chiefly the 
external and internal arciform fibers. 18 The anterior exter- 
nal arciform fibers 19 rise in the nucleus gracilis and nucleus 
cuneatus of the opposite side, decussate in the raphe and issue 
from the anterior median fissure and ventral surface of the 
medulla, whence they have been trnced over the surface to 
the restiform body. Perhaps a few nre interrupted in the 
external arciform nucleus. The posterior rxfernnl arciform 
fibers 19 rise from the same nnclei and enfor (he cerebellum, 
through the inferior peduncle, without decussation. "Rotli 
groups of fibers end in the cortex of the vermis cerebelli 
superior. The internal arciform fibers are contained in flv 
formatio reticularis. Thev ;ire disposed in two groups. \ ; 

(IS) Fibre nroimtnp. 

(10) Fibre areuatse externa anterior, posterior. 



I36 THE BRAIN AND SPINAL CORD. 

those of the sensory decussation, and those of the olivary 
peduncle. 

The fibers of the sensory decussation 20 rise chiefly from 
the nucleus gracilis and nucleus cuneatus. Bending ventrally 
through the posterior horn of gray matter, they decussate 
through the median raphe; and, then, the greater number 
run forward toward the cerebrum as the medial and superior 
fillets ; the remainder constitute the deep part of the anterior 
external arciform fibers. The sensory, or fillet, decussation 
is nearer the pons and dorsal to the decussation of the 
pyramids. 

The olivary peduncle is a sheet of fibers extending between 
the two olivary nuclei of the medulla. It is the inferior por- 
tion of the cerebello-olivary tract. 21 It is composed of axones 
from Purldnje's cells. Descending: to the medulla thronsrh 
the inferior cerebellar peduncle, it pierces the olive, crosses 
through the raphe and terminates in the olivary bodv of the 
opposite side. The cerebello-olivarv tract connects the 
cerebellar hemisphere with the opposite nucleus. 

(2) The Dorso-ventral Fibers of the medulla are found 
in three situations: (a) in the raphe, (b) between the 
anterior and lateral areas, and (c) between the lateral and 
posterior areas. 

(a) The dorso-ventral fibers of the raphe are the anterior 
external arciform fibers. These can be traced to the cere- 
bellum through the restiform body. Their origin is chiefly 
in the nuclei gracilis et cuneatus. Some of them seem to be 
interrupted in the arciform nuclei on the ventral surface of 
the pyramids. The root-bundles of the eighth to the twelfth 
cranial nerves constitute the remaining groups of dorso- 
ventral fibers. By them the medulla is divided into areas. 

(20) Decussatio lemniscorum. (21) Fibrse cerebello-olivares. 



THE AFTER-BRAIN. I 37 

(b) The root-bundles of the hypoglossal nerve 22 run from 
the ventricular gray matter, near the median line, ventro- 
laterally to the ventro-lateral groove, where they emerge. 
Inclosing between them and the raphe, the anterior area, they 
also separate it from the lateral area, The anterior and 
lateral areas are bounded dorsally by the thick sheet of gray 
matter in the floor of the fourth ventricle. 

(c) The medial root 23 of the auditory nerve, the roots of 
glosso-pharyngeal 24 and vagus 25 and the accessory root of the 
eleventh 26 form the third group of dor so-ventral fibers. From 
the dorso-lateral groove, which is their superficial origin, 
they may be traced through the medulla to ventricular gray 
matter external to the column of cells from which the twelfth 
nerve rises. They separate the lateral from the posterior 
area, The posterior area comprises everything dorsal to the 
above roots of the eighth to eleventh cranial nerves. It thus 
includes the gray matter in the floor of the fourth ventricle. 

(3) Longitudinal Fibers.— In the medulla, the longitu- 
dinal fibers are chiefly continuations of the same in the spinal 
cord. They can be best located by reference to the ihvcc 
areas, bounded by the above dorso-ventral fibers, namely 3 
Anterior, Lateral and Posterior areas. 

ANTERIOR AREA. 

The anterior area of the medulla lies between the raphe 
and the roots of the hypoglossal nerve, and between the 
ventral surface and the gray matter in the floor of the fourth 
ventricle. Excepting that part forming the crossed pyram- 
idal tract and the interolivary fillet, it is continued in the 

(22) Nervus hypoglossals. 

(23) Radix nervi vestibularis. 

(24) "Radix nervi grlossopharyngel. 

(25) Radix nervi vagi. 

(26) Radix cerebralis nervi accessorii. 



T38 THE BRAIN AND SPINAL CORD. 

anterior column of the spinal cord. It is naturally divided 
into a ventral and a dorsal part, or the region of the pyra- 
mid 27 and the region of the formatio reticularis alba. 

The 'pyramid, with the external arciform nucleus imbedded 
in it, occupies the ventral portion of the anterior area. It is 
the continuation of the pyramidal tract and is composed of 
the axones of cortical cells in the Kolandic region of the 
cerebrum. The pyramidal tract diminishes in size as it 
descends through the pons and medulla, because some of its 
fibers terminate in ramifications about the cells of cranial 
nerve-nuclei. In the lower part of the medulla, the pyramid 
breaks up into the uncrossed (direct) pyramidal tract 28 (10 
to 20 per cent of the pyramid), which descends along the 
anterior median fissure in the same side of the spinal cord: 
and the crossed pyramidal tract 29 (80 to 90 per cent of the 
pyramid), which, after decussating with its fellow through 
the anterior median fissure, runs down in the lateral column 
of the opposite side of the cord. The fibers of the direct 
tract cross in succession to the opposite side of the cord, 
through the anterior, or white, commissure ; and there, with 
the fibers of the crossed pyramidal tract, terminate in fibrillar 
end-tufts about the cell-bodies in the anterior cornu of gray 
matter. Thus the pyramid forms a crossed cerebral tract 
for efferent (motor) cranial and spinal nerves. A small 
number of pyramidal fibers (20 per cent, Marchi) descend in 
the lateral column of the cord without decussation. They 
account for the weakness on the well side and for slight 
motion on the paralyzed side, which are commonly observed 
in hemiplegia. 

(27) Pyramis medullae oblongatse. 

(28) Fasciculus cerebro-spinalis anterior (ventralis). 

(29) Fasciculus cerebro-spinalis lateralis. 



THE AFTER-BRAIN. I 39 

The dorsal part of the anterior area is occupied by the 
formatio reticularis alba. Gray matter from the anterior 
horn is sparsely scattered throughout the reticular formation, 
but it contains the bodies of very few nerve cells and is of a 
light color. The internal accessory olivary nucleus is im- 
bedded in it near the pyramid and among the fibers of the 
fillet; and three definite bundles of longitudinal fibers have 
been demonstrated in it, namely, the Interolivary Fillet, the 
Posterior and the Anterior longitudinal bundles. 

Interolivary Fillet. — Just dorsal to the pyramid in the 
anterior area of the medulla, is a large bundle of fibers called 
the interolivary fillet. 30 Situated between the inferior oli- 
vary bodies, it is on that account called the interolivary fillet. 
Superiorly, it is continued in the medial and superior 
fillets. 31 The interolivary fillet rises from the nucleus gracilis 
and nucleus cuneatus of the medulla and crosses through the 
median raphe in the sensory decussation. As the fillet runs 
brainward through the reticular formation of the pons and 
mid-brain, it receives fibers from the terminal nuclei of 
sensory cranial nerves, except the cochlear nuclei, and from 
the middle peduncles of the cerebellum. Externally, it is 
accompanied for a short distance in the pons by the lateral 
fillet. 32 The interolivary fillet is composed of ascending 
axones which constitute a "cerebral" tract for the afferent; or 
sensory, fibers of spinal and cranial nerves. It carries 
ordinary sensations to the anterior quadrigeminal body, by 
the superior fillet, and to the optic thalamus by the media] 
fillet. 

The posterior longitudinal bundle^ is a small fasciculus 

(30) Lemniscus inter olivaris. 

(31) Lemniscus medialis el lemniscus superior. 

(32) Lemniscus lateralis. 

(33) Fasciculus longitudinalis medialis. 



140 THE BRAIN AND SPINAL CORD. 

composed of fibers continued up from the anterior column of 
the spinal cord. Its origin is in the anterior horn of gray 
matter. In the medulla it runs along the median raphe in 
contact with the ventricular gray matter, and is augmented 
in the medulla and pons by fibers from the terminal nuclei 
of the sensory cranial nerves and by fibers from the nuclei of 
the abducent nerves and the middle cerebellar peduncle. 
Further forward, some of these fibers and others of spinal 
origin leave the bundle to end, chiefly on the opposite side, in 
the motor cranial nerve-nuclei, especially the third. Fibers 
join the posterior longitudinal bundle in the mid-brain from 
the motor oculi nucleus, and descend to the genu of the 
facial nerve. The posterior longitudinal bundle ends, supe- 
riorly, in the thalamus or hypothalamus. It associates spinal 
and cranial nerves with one another, forming part of a reflex 
arc. It also connects the cerebellum with opposite cranial 
nuclei and probably conducts ordinary sensation to the 
thalamus (see Mid-Brain). 

Anterior Longitudinal Bundle. — The pupillo-dilator 
tract 34 rises from the anterior quadrigeminal body, and is 
seen just ventral to the posterior longitudinal bundle, which 
it accompanies all the way down to its termination in the 
cervical cord (see Mid-Brain). 

LATERAL AREA. 

Contents: Superficially, the antero-lateral ground bundle 
and antero-lateral descending and ascending cerebellar tracts; 
deeply, the formatio reticularis grisea. Imbedded in the 
formatio reticularis are the nucleus ambiguus, the lateral 
nucleus, the olivary nucleus and external accessory olivary 
nucleus. 

The gray matter of the formatio reticularis grisea is a 

(34) Fasciculus longitudinalis ventralis. 



THE AFTER-BRAIN. I4I 

part of the disintegrated anterior gray horn and, unlike that 
of the anterior area, it contains the bodies of many large 
nerve cells. 

Antero-lateral Ground Bundle. 35 — The whole lateral col- 
umn of the spinal cord, except the crossed pyramidal and 
direct cerebellar tracts, is continued into the lateral area of 
the medulla, Composed of ascending and descending axones 
which are commissural and associative for different segments 
of the spinal cord, the lateral ground bundle ascends into 
the medulla, and runs in part beneath and in part superficial 
to the olivary nucleus; beyond the olive, it is continued in 
the formatio reticularis grisea of the medulla and reticular 
formation of pons and mid-brain. Among the fibers of 
the antero-lateral ground bundle, ventral to the olive, is the 
triangular tract 36 of Helwig and, dorsal to the olive, the 
olivary bundle. The former is believed to end in the olive of 
the medulla and the latter to rise from it. They are made 
up of ascending axones and, according to Bechterew, form a 
functionally continuous tract. 

The antero-lateral descending cerebellar tract 37 rises in the 
cerebellar cortex. It forms part of the inferior peduncle of 
the cerebellum, through which it reaches the medulla. In 
the lateral area, it descends along the ventro-lateral groove, 
between the lateral tract and pyramid, to the corresponding 
area of the cord. It ends in the anterior cornu of gra\ 
matter. Fibers from the cerebral cortex are scattered 
through the bundle in the cord, and it was once regarded as 
a part of the direct pyramidal tract. 

Antero-lateral Ascending Cerebellar Tract 31 — Taking its 

(35) Fasciculus proprius antero-lateralis. 

(36) Tractus tricugularis (Helwigi). 

(37) Fasciculus anterolateralis superiicialis, deseondens and as- 
cendens. 



142 THE BRAIN AND SPINAL CORD. 

origin from the base of the anterior cornu and center of the 
crescent of gray matter, chiefly on the opposite side of the 
spinal cord, and crossing through the anterior commissure, it 
ascends mingled with the fibers of the above descending 
tract, along the lateral surface of the cord. It runs along 
the dorso-lateral groove and through the formatio reticularis 
of the medulla and pons; and then, turning backward, it 
reaches the cerebellar worm through the superior peduncle 
and the valve of Vieussens. A small bundle of its fibers 
winds over the superior cerebellar peduncle, and joins the 
lateral fillet in its course to the posterior quadrigeminal 
body; that bundle ends in the optic thalamus. The antero- 
lateral ascending cerebellar tract is closely related to the 
direct cerebellar tract. Both carry sensory impulses to the 
vermis cerebelli superior. 

The crossed descending tract of the red nucleus, running 
dorsal to the inferior olive, is mingled with the fibers of the 
antero-lateral ascending cerebellar tract, in the medulla; it 
continues down the cord, in the dorso-lateral portion of the 
crossed pyramidal tract, to the lateral horn and center of the 
gray crescent as far as the first lumbar segment. 

POSTERIOR AREA. 

The longitudinal fibers of the posterior area form many 
bundles; and the bundles are different in upper and lower 
medulla. The formatio reticularis is small, but is present 
throughout this area. 

The lower, or closed, medulla contains: the Fasciculus 
gracilis, 38 Fasciculus cuneatus, 39 Fasciculus of Rolando and 
Direct cerebellar tract (named from the posterior median 
fissure outward). In the upper or ventricular medulla are: 

(38) Fasciculus gracilis. 

(39) Fasciculus cuneatus. 



THE AFTER-BRAIN. 143 

the Eestiform body, at the surface; and the Inferior (or 
spinal) root of the fifth cranial nerve, the Fasciculus soli- 
tarius and Fasciculus teres in the interior. 

The fasciculus gracilis is the superior end of the postero- 
median column ( Golfs column) of the spinal cord. Near 
its extremity it expands and forms the clava, and then tapers 
off and disappears along the side of the fourth ventricle. 
The clava is due to the nucleus gracilis, in which the fibers of 
the column end. A small number of fibers continue, without 
interruption, into the fillet and external arciform fibers 
Like the cuneate column, the fasciculus gracilis is composed 
of ascending branches of the posterior roots of the spinal 
nerves. 

Fasciculus cuneatus. — It is separated from the posterior 
median fissure by the gracile bundle ; and is the continuation 
of the greater portion of the postero-lateral column (Bur- 
dach's column) of the spinal cord. It ends about the cells 
of the nucleus cuneatus and accessory nucleus onneatns. 
which form the cuneate tubercle seen on the surface. A few 
fibers from this bundle are directly continued in the inter- 
olivary fillet, and two small bundles, inclosing the inferior 
(or spinal) root of the fifth nerve, run as posterior external 
arciform fibers to the cerebellum. The fibers of the fas- 
ciculus cuneatus 40 are ascending branches of the posterior 
roots of the spinal nerves. 

Fasciculus of Rolando — From the cnneato column, a small 
bundle of fibers, taking a more lateral course, runs over and 
ends within the nucleus of "Rolando. Tt constitutes the fas- 
ciculus "Rolandi. This column is not separately represented 
in the spinal cord. The nucleus of "Rolando, in which it 
terminates, is situated beneath the restiform body. The 

(40) Fasciculus cuneatus. 



144 THE BRAIN AND SPINAL CORD. 

nucleus causes a slight eminence on the surface called the 
tuberculum Eolandi. 

The direct cerebellar tract 41 in the lower medulla crosses 
the dorso-lateral groove, from the lateral column of the core! 
to the posterior area of the medulla; it then ascends to form 
a large part of the restiform body, the inferior peduncle of 
the cerebellum. It takes its origin from the vesicular column 
of Clark in the spinal cord. It ends in the superior cerebellar 
worm. 

Restiform Body.- — In the upper medulla, forming the 
lateral part of each posterior area, is a large rounded bundle 
of fibers, called the restiform body. 42 It is the largest bundle 
in the medulla. Forming the inferior peduncle of the cere- 
bellum, it terminates in the cerebellar cortex of both the 
hemisphere and worm. It is made up of the following: 
Ascending- — (1) Direct cerebellar tract; (2) External arci- 
form fibers, anterior and posterior; (3) The acustico-cere- 
bellar tract from the nuclei of the vestibular nerve to the 
nucleus fastigii and nucleus globosus of the opposite side; 
and (4) A tract from the lateral nucleus to the same side 
of the cerebellum. Descending — (1) Antero-lateral de- 
scending cerebellar tract, and (2) The cerebello-olivary tract, 
which ends in the inferior olive opposite to its origin. 

The restiform body is inclosed between the medial and 
lateral roots of the auditory nerve (eighth). 43 Ventral to 
it and between the roots, is the ventral part of the cochlear 
nucleus; on its lateral surface and among the fibers of the 
lateral root, is the dorsal, or lateral, part of the same 
nucleus. The vestibular nuclei, the dorso-medial (Schwalbe). 
the dorso-lateral (Deiter). and the superior (Flechsig and 

(41) Fasciculus cerebellospinal. 

(42) Corpus restiforme. 

(43) Nervus acusticus. 



THE AFTER-BRAIN. 145 

Bechterew) are situated dorsal and medial to the restiform 
body. 

The inferior root of the fifth nerve** is the main sensory 
root. It leaves the superior sensory root in the pons; and, 
running down in the lateral portion of the posterior area, 
it terminates ventral to the restiform body about the cells of 
the nucleus Eolandi. 

Fasciculus Solitarious. — The respiratory bundle is a small, 
round bundle imbedded in the middle of the ventricular gray 
matter of the posterior area. It forms an accessory sensory 
root for the ninth and tenth cranial nerves. It descends near 
the main nuclei of those nerves and along 1 the medial aspect 
of the posterior horn of gray matter in the cord. It ends on 
both sides of the median line in the grav matter along its 
course. The solitary bundle may be traced from the upper 
part of the medulla down to the eighth cervical segment of 
the spinal cord CCajal). Many of its fibers cross through 
the raphe and, after giving off collaterals to the interolivarv 
fillet, terminate about cells on the opposite side. It is be- 
lieved to associate the nuclei of the nerves controlling the 
muscles of respiration, hence the synonym, respiratory bundle. 

Fasciculus Teres. — On either side of the median lino and 
extending almost the whole length of the floor of the fourth 
ventricle, is a lozenge-shaped eminence, called the fasci- 
culus teres. In the pontine part of the ventricular floor, it 
ends as the eminentia teres. Tt taper? off to a point in the 
posterior angle of the ventricle (hypoglossal trigone), and 
the two together form the nibs of a ^o^. the calamus 
scriptorius. It is composed of a flat band of fibers covering 
the hypoglossal nucleus, posteriorly, and the terete and the 
abducent nucleus, anteriorly. The ascending portion 

(44) Radix spinalis nervl trlgeminl. 



I46 THE BRAIN AND SPINAL CORD. 

(genu) of the root of the facial (or 7th) nerve and fibers 
from the formatio reticularis make up the fasciculus teres. 

GRAY MATTER. 

The gray matter of the medulla is composed, (1) of that 
continued up from the spinal cord, and (2) of added nuclei 
not represented in th cord. 

(1) By the dilation of the central canal of the spinal 
cord forming the fourth ventricle, the posterior cornua of 
the H-shaped column of gray matter are pushed outward to 
a transverse direction; and the bases of the anterior cornua 
are brought into the floor of the ventricle. The expansion 
of the canal, together with the decussation of the crossed 
P30"amidal tracts through the anterior cornua and of the in- 
terolivary fillets through the posterior and anterior cornua, 
disposes the H-shaped column as follows: 

Anterior Horn. — From the base of the anterior cornu 45 
is derived a column of cells, the hypoglossal nucleus, which 
lies along the median raphe beneath the fasciculus teres. 
The head of the anterior cornu is broken up by the crossed 
P3rramidal tract into the nucleus lateralis, in the lateral area, 
near the dorso-lateral groove; and the nucleus ambiguus, a 
large column of cells, coinciding in extent with the inferior 
olive, and seen as a pear-shaped mass in the lateral area, 
which is the motor nucleus for the ninth, tenth and acces- 
sory part of the eleventh cranial nerves. The lateral nucleus 
is probably terminal to certain fibers in the antero-lateral 
ascending cerebellar tract, and it gives rise to a tract of 
fibers which runs through the restiform body to the cortex 
in the same side of the cerebellum. The gray matter of the 
formatio reticularis alba et grisea belongs to the anterior 

(45) Columna anterior. 



THE AFTER-BRAIN. 147 

cornu. It is of a light color (alba) m the anterior area, 
where there are the bodies of but few cells. In the lateral 
area the cell-bodies are numerous and the color in gray 
(grisea). 

The Posterior Horn* G is decapitated by the fillet. Its 
base forms a column of cells, external to the nucleus am- 
biguus and hypoglossal nucleus, which contains the chief 
sensory nucleus of the pneumogastric (10th) of the glosso- 
pharyngeal (9th), and of a part of the auditory (8th) 
nerves. It forms likewise the accessory cuneate nucleus. 
The head of the posterior horn forms the nucleus of Ro- 
lando. That nucleus is the inferior sensory nucleus of the 
trifacial (5th) nerve. In it the so-called ascending root of 
the fifth terminates. The posterior horn furnishes the gray 
matter for the reticular formation of the posterior area. 

It should be noted that the chief nuclei derived from the 
H-shaped column lie in the floor of the fourth ventricle. 

(2) Added Nuclei. — The medullary gray matter not 
represented in the spinal cord makes up the following nuclei : 
Nucleus gracilis, nucleus cuneatus, olivary nuclei, and 
nucleus of external arciform fibers. 

Nucleus Gracilis and Nucleus Cuneatus. — They are situ- 
ated near the dorsal surface of the medulla, beneath the gra- 
cile and cuneate bundles, whose fibers terminate in them; 
they give origin to the interolivary fillet and the anterior 
and posterior external archiform fibers, the two former con- 
stituting the sensory decussation; and they produce, re- 
spectively, the clava and cuneate tubercle. 47 The accessory 
cuneate nucleus is a continuation of the vesicular column of 
Clark at the base of the posterior gray horn in the spinal 
cord. From it a small fasciculus rises which, as posterior 

(46) Columna posterior. (47) Tubeivulum cuneatum. 



I48 THE BRAIN AND SPINAL CORD. 

external archiform fibers, runs within the restiform body 
to the cerebellum. The nucleus gracilis and cuneatus are 
connected with the posterior cornu, but have no representa- 
tive in the cord. 

The Olivary Nucleus** of the medulla (inferior olivary 
nucleus) is a sinuous, pouch-like collection of gray matter 
resembling the corpus dentatum of the cerebellum. It is 
situated near the lateral surface of the medulla, and is in- 
vested superficially and deeply by fibers from the antero- 
lateral ground bundle. Its open hilum looks medially and 
is filled with fibers, the cerebello-olivary tract, 49 which join 
it to the opposite hemisphere of the cerebellum. On either 
side of the olivary nucleus is an accessory nucleus — the in- 
ternal accessory, 50 in the anterior area among the fibers of 
the inter-olivary fillet, and the external accessory, 51 in the 
lateral area. The olivary nucleus, covered by fibers of the 
antero-lateral ground bundle, forms the olivary body (oliva). 
The triangular tract of Helwig, or the olivary bundle of the 
spinal cord, enters the ventral surface of the olivary body 
and is believed to terminate in it. The olivary bundle of the 
brain, the central tegmental tract, appears to rise from the 
olive in the medulla and to continue the ascending conduc- 
tion tract to the globus pallidus of the lenticular nucleus 
(Flechsig). The latter tract is situated just dorsal to the 
olive. The inferior olive receives two tracts of descending 
fibers, namely, the vestibulo-olivary and the cerebello-olivary. 
And according to Koelliker, it gives origin to axones which 
descend through the lateral column of the spinal cord to the 
anterior gray cornu. 

(48) Nucleus olivaris. 

(49) Fibrae cerebello-olivares. 

(50) Nucleus olivaris accessorius medialis. 

(51) Nucleus olivaris accessorius dorsalis. 



THE AFTER-BRAIN. 1 49 

Nucleus of the External Arciform Fibers. — There are sev- 
eral masses of gray matter, containing the bodies of nerve 
cells, scattered among the anterior external arciform fibers. 
Of these the largest mass is near the ventral surface of the 
pyramid. It is called the arciform nucleus. 52 

Lesions in the medulla are very fatal and death usually 
occurs before any sensory. or motor phenomena can be ob- 
served; but rarely the pyramidal tracts alone have been in- 
volved or the pyramidal tracts together with one or more of 
the roots of the ninth to the twelfth cranial nerves. In the 
last case, crossed paralysis is produced, affecting the cranial 
nerves on the same side and the opposite spinal nerves. In 
progressive bulbar paralysis the motor nuclei of the medulla 
are involved as a preliminary to the degeneration of the an- 
terior gray cornu in the spinal cord ( Grlossolabio-laryngeal 
paralysis). 

(52) Nucleus arcuatus. 



CHAPTER VII. 

FOURTH VENTRICLE. 

The common cavity of the hind-brain and after-brain is 
the fourth ventricle. 1 The fourth ventricle is contained in 
the pons and medulla, and is ventral to the cerebellum. It 
is broadest at the junction of the pons and medulla. Above 
and below that junction, it contracts to the size of the aque- 
duct of Sylvius and central canal of the spinal cord, with 
which it is continuous. Dorsally, it communicates with the 
subarachnoid space through three foramina (Magendie, and 
Key and Retzius). It is a gable-roofed cavity with a dia- 
mond-shaped floor. The long axis of the floor is parallel 
with the spinal cord, and extends from the anterior extrem- 
ity of the pons to the middle of the medulla. The transverse 
axis coincides with the junction of the pons and medulla. 
Thus the anterior triangle of the floor is formed by the pons ; 
the posterior, by the medulla oblongata. The fourth ventri- 
cle is lined with ependyma, which is complete throughout, 
except in the roof of the posterior part, where only the 
epithelial layer is present. 

Boundaries. — The floor is formed by the pons and me- 
dulla. The lateral walls (anterior triangle) are formed by 
the superior peduncles 2 of the cerebellum; and (posterior 
triangle) by the inferior cerebellar peduncles, 3 fasciculus 
cuneatus and fasciculus gracilis. The roof is formed by the 
valve of Vieussens, 4 anteriorly; and the inferior medullary 

(1) Ventriculus quartus. (3) Corpora restiformia. 

(2) Brachia conjunctiva. (4) Velum medulare anterius. 



FOURTH VENTRICLE. 151 

velum and roof epithelium, posteriorly. The anterior and 
posterior halves of the roof meet at an acute angle and form 
the tent 5 of the fourth ventricle. On either side, the tent 
extends over the restiform body into the lateral recess. The 
lateral recess is a tunnel-like extension of the ventricular 
cavity. It is bounded, superiorly and ventrally, by the in- 
ferior cerebellar peduncle; dorsally, by the inferior medul- 
lary velum; and inferiorly, by the roof epithelium. The 
choroid plexuses 6 of the fourth ventricle invaginate the roof 
epithelium and hang from the roof in the posterior part of 
the cavity. 

Floor of the Fourth Ventricle. — Because of the origin of 
one or more roots of the posterior eight (fifth to twelfth) 
cranial nerves from the floor of the fourth ventricle, it is 
a very important area. A median groove 7 forming the long 
axis of the diamond-shaped floor, divides it in two lateral 
halves, which are bisected transversely by a number of lines, 
the acustic striae. 8 The acustic striae are produced by bundles 
of fibers which enter or issue from the median groove, being 
partly continuous with dorso-ventral fibers in the raphe. 
They run across the floor of the ventricle. In part they arc 
continuous with the lateral root of the auditory nerve ; but. 
the greater number are connected with the flocculus. They 
divide each lateral half of the floor into anterior and pos- 
terior triangle. 

The anterior triangle of the floor presents the eminentia 
teres, superior fovea, locus coeruleus and a part of the acus- 
tic trigone. 

(5) Fastigium. 

(6) Plexus choroideus ventriculi quartl. 

(7) Sulcus longitudinalis fossae rhomboidese. 

(8) Strlse medullares. 



I s2 THE BRAIN AND SPINAL CORD. 

The eminentia teres.'-' the anterior extremity of the fascic- 
ulus teres/ is located next the median groove. Beneath 
it are the nucleus teres (accessor}?" to ninth and tenth cranial 
nerves), and nucleus of the abducent (sixth) nerve. Ex- 
ternal to it and in front of the striae acusticae is a small 
fossa, the fovea superior. 

The Fovea Superior. — The fovea superior is near the lat- 
eral wall of the ventricle and marks the location of the facial 
(seventh) nucleus, which is deeply seated in the pons. Kun- 
ning forward and medially along the wall of the ventricle 
from the superior fovea, is a blue-floored groove, called locus 
coeruleus. 

The locus coeruleus continues to the anterior angle of 
the ventricle. The color of the locus coeruleus is due to the 
substantia ferruginea, a pigmented layer of cell-bodies un- 
derlying it. The principal motor nucleus of the trifacial, 
or fifth, nerve lies beneath the anterior part of the locus 
coeruleus. 

Posterior Triangle of the Ventricular Floor. — It presents : 
the hypoglossal trigone, trigonum vagi (fovea inferior, ala 
cinerea and eminentia cinerea) and most of the trigonum 
acustici. 

The hypoglossal trigone 11 is the posterior half of the fas- 
ciculus teres. Its apex is in the posterior angle of the ven- 
tricle, and forms a nib of the calamus scriptorius ; its base 
looks forward and is situated under the acustic striae. The 
twelfth nerve rises from the column of cells covered by it. 
External to the trigonum hypoglossi and posterior to the 
acustic striae is the inferior fovea, which forms the apex of 
the trigonum vagi. 

(9) Colliculus facialis. 

(10) Eminentia medialis. 

(11) Trigonum nervl hypoglossi. 



FOURTH VENTRICLE. 153 

Trigonum Vagi. — The pneumogastric trigone is of a 
darker color than the ventricular floor aronnd it, and is often 
called the ala cinerea. The inferior fovea forms the de- 
pressed and anteriorly directed apex of the triangle ; its floor 
rises posteriorly to the base, eminentia cinerea, which abuts 
against the lateral wall of the ventricle. The principal 
nuclei of the glosso-pharngeal (or ninth) and the pneumo- 
gastric (or tenth) nerves are situated, respectively, beneath 
the fovea inferior and trigonum vagi. 

The trigonum acustici 12 occupies the lateral angle of the 
ventricular floor. It is partly in the anterior triangle, but 
chiefly in the posterior. Inclosed between the trigonum vagi 
and the ligula, its apex points backward, and its base looks 
forward and is crossed by the acustic striae. A slight tuber- 
cle, eminentia acusticaa, makes the base of the trigone, in 
the lateral angle most prominent. Beneath the acustic tri- 
gone is the dorsal, or vestibular, nucleus of the auditory 
nerve; also the dorsal part of the cochlear nucleus, which is 
found in the acustic tubercle. 

ORIGIN OF CRANIAL NERVES. 

According to Soemmering, there are twelve pairs of cranial 
nerves. Their origins (or terminations) are superficial and 
deep. The meaning of Superficial (apparent) origin, as 
commonly used, is the point of attachment of a nerve to the 
brain or cord surface; Deep (real) origin signifies the deep- 
est point to which the fiber? of a nerve can be traced. For 
motor nerves this nomenclature is correct, the deep origin 
being the nucleus in which the fiber? rise that form the 
nerve; but it is exactly opposite to the truth for sensory 
nerves. The so-called deep origin of a sensory nerve is 
actually the terminal nucleus in which the fibers of the nerve 

(12) Area acustica. 



154 



THE BRAIN AND SPINAL CORD. 



arborize and end. 
following table. 



With these facts in mind examine the 



TABLE II. 



Name. 



1. Olfactory 13 
(Smell) 



Superficial origin, 
or termination. 



Nerves 
bulb, 



. Olfactory 
surface 



Deep origin, or 
termination. 

Stratum glomeru- 
losum of olfac- 
tory bulb. 



f Gyrus fornicatus. 
I Trigonum olfac- 
Tract. Three roots <j torii. 

Uncus hippocam- 
l pi. 



; { 



' Nerve. Optic 
commissure 



2. Optic" <| 



Tract 



Optic tha- 
lamus, ex- 
ternal and 
internal 
geniculate 
bodies, an- 
t e r i o r 
quadrige- 
m i n a 1 
body 



Outer root — Ex- 
ternal geniculate 
body, optic tha- 
lamus, Anterior 
or quadrigemin- 
al body. 

Inner root — Optic 
thalamus, Inter- 
nal geniculate 
body. 



3. Oculomotor 15 
(Motor) 



J Interpeduncular 
fossa 



4. Trochlear 18 



Valve of Vieus- 
sens 



Floor of Sylvian 
aqueduct. 



Floor of Sylvian 
aqueduct. 



(13) Nervus olfactorius. 

(14) Nervus opticus. 



(15) Nervus oculomotorius. 

(16) Nervus trochlearis. 



FOURTH VENTRICLE, 



155 



5. Trifacial 17 

(M. Sensory) 



Pons, ventral sur 
face 



6. Abducent 18 
(M.) 



7. Facial" 
(M.) 



Pars intermedia 20 . 
(Taste) 



Groove between 
pons and me- 
dulla 



Groove between 
pons and me- 
dulla 



Between facial 
and auditory. 



8. Auditory 21 

(Hearing and 
space-sense) 



{ 



Groove between 
pons and m 
dulla 



Motor root — Floor 
of fourth ventri- 
cle, and Sylvi- 
an aqueduct. 

Sensory root — 
Under superior 
cerebellar pe- 
duncle in pons, 
and Nucleus of 
Rolando in me- 
dulla. 

Floor of fourth 
ventricle be- 

neath eminentia 
teres. 

Floor of fourth 
ventricle be- 

neath superior 
fovea. 

Beneath inferior 
fovea. 

Vestibular root — 
Vestibular (or 
Dorsal) nucleus 
in ventricular 
floor, Spinal nu- 
cleus in cord. 
Nucleus fastigii 
and nucleus glo- 
bosus in cerebel- 
lum. 

Cochlear root — 
Cochlear (or 

ventral) nucleus 
(ventral and 
dorsal parts) in 
dorso - lateral 
groove and on 
la torn! surface of 
restiform body, 
and various nu- 
clei up to pos- 
terior cpiadrige- 
minal body. 



(17) Nervus trigeminus. 

(18) Nervus abducens. 

(19) Nervus facialis. 



(L'O) Nervus intermedius. 
(21) Nervus acustlcua. 



156 THE BRAIN AND SPINAL. CORD. 

f Dorso-lateral 

9. Glossopharyngeal 22 J groove of me- f Ventricular floor, 

(M. S. and ^ dulla J posterior trian- 

taste) I gle beneath fo- 

^ _ . vea inferior. 

r Dorso-lateral k 

10. Pneumogastric 23 . . J groove of me- r 

(M. S.) dulla "..J Ventricular floor, 

trigonum vagi. 

11. Spinal accessory 2 

( M -) oc r Dorso-lateral 

Accessory root 25 ... j gr0 ove of me- 

dulla <! Closed medulla. 



r Dorso-lateral 
J groove of me- r 
\ dulla J 



Spinal root 28 J Lateral column of r intermedio - later- 

1 spinal cord.... J al co iumn of 

L cells in cord. 
< Ventro-lateral 

12. Hypoglossal 27 J groove of me- < Ventricular floor 

< M -) I dull a '.-.J beneath trigo- 

L num hypoglossi. 

The posterior ten cranial nerves rise from two series of 
nuclei — (1) a ventral or anterior and (2) a dorsal or pos- 
terior series. The ventral series corresponds to the anterior 
cornu of gray matter in the spinal cord. It is entirely motor 
or efferent. The dorsal is regarded as a continuation of the 
posterior cornu and is sensory or afferent in function. Each 
series is composed of a double chain of nuclei: (a) a medial 
chain, derived from the base of the cornu and (b) a lateral 
chain, from the caput cornu. 

(1) Ventral Series, Motor. 

(a) The Medial Chain is close to the median line, be- 
neath the fasciculus teres and aqueduct of Sylvius. It gives 
origin to the Hypoglossal (12th), Abducent (6th), Troch- 
lear (4th), and Oculomotor (3rd) nerves; also to accessory 

(22) Nervus glossopharyngeus. (25) Radix cerebralis. 

(23) Nervus vagus. (26) Radix spinalis. 

(24) Nervus accessorius. (27) N. hypoglossus. 



FOURTH VENTRICLE. 1 57 

motor roots of the 10th. and 9th nerves in the nucleus teres; 
and to the 5th in the floor of the Sylvian aqueduct. All are 
efferent or motor. 

(b) Lateral Chain. — This also is motor. It lies external 
to the medial chair, beneath the internal parts of the locus 
coeruleus and trigonum vagi. Converging slightly toward 
its fellow of the opposite side it extends backward into the 
closed medulla. It is regarded as the head of the anterior 
cornu. From the lateral chain of the ventral series rise: 
the accessory root of the spinal accessory (11th), posterior 
to the fourth ventricle ; the chief motor roots of the Pneumo- 
gastric (10th) and Glossopharyngeal (9th) ; the root of the 
Facial (7th) ; and the principal motor root of the Trifacial 
(5th). The motor roots of the 11th, 10th and 9th nerves 
rise from the nucleus ambiguus. 

(2) Doesal Sebies, Sensory. 

(a) Medial Chain of Nuclei. — It corresponds to the base 
of the posterior gray cornu. Placed external to the ventral 
series, it is covered by the lateral part of the trigonum vagi, 
the acustic trigone and superior peduncle of the cerebellum. 
It is entirely sensory or afferent, and it contains the princi- 
pal sensory nuclei of the Pneumogastric (10th), and Glosso- 
pharyngeal (9th) ; the dorsal (vestibular) nucleus of the 
Auditory (8th) ; and the superior sensory nucleus of the 
Trifacial (5th). 

(b) The Lateral Chain of the dorsal series is most ex- 
ternal in position. It is located beneath the tubercle of Ro- 
lando and the restiform body. In it are contained the in- 
ferior sensory nucleus of the trifacial (5th), called the 
nucleus of Rolando; and the ventral (accessory) and lateral 
nuclei (the cochlear nuclei) of the eighth, or auditory nerve. 
These nuclei are sensory or afferent. 



I58 THE BRAIN AND SPINAL CORD. 

The Olfactory (1st) and the Optic (2nd) are sensory, or 
afferent, and probably belong to the dorsal nerves, but this 
is difficult of demonstration. 

BLOOD SUPPLY OP THE MEDULLA OBLONGATA. 

Branches of the posterior inferior cerebellar artery, the 
vertebral and the anterior spinal supply the medulla. The 
first supplies the choroid tela. The branches to the nerve 
substance enter the median raphe or follow the roots of the 
burbar nerves, suggesting the centrifugal and centripetal 
arteries of the spinal cord. The veins pursue the same course 
as the arteries. Both arteries and veins possess the perivascu- 
lar lymph spaces. There are no lymphatic vessels. 



CHAPTER VIII. 



MEMBRANES OF THE SPINAL CORD. 

Dura Mater. — Through the foramen magmim the mem- 
branes of the cord are continuous with those of the brain with 
which they are very similar in structure. The dura mater 1 
is attached to the margin of the great foramen and to the 
bodies of the first two or three cervical vertebrae, elsewhere 
its surface is free from bony attachment and does not pos- 
sess the periosteal layer. Thus suspended, it hangs as an 
open sack, or sheath, and reaches down to the third sacral 
vertebra, where it is contracted to a fibrous cord which blends 
with the periosteum on the posterior surface of the coccvx. 

The spinal cord and the cauda equina are contained in 
the dural sack. Externally, the surface of the dura is separ- 
ated from the wall of the spinal canal by the meningo- 
rachidian veins, 2 areolar tissue and fat. It is composed of flat 
polygonal cells, like the inner surface. Its internal, serous 
surface is bathed with a small amount of cerebrospinal 
fluid which separates it from the Arachnoid. For every seg- 
ment of the spinal cord, it presents, on either side, a pair of 
foramina, through which run the anterior and posterior roots 
of the spinal nerves. Those nerve roots are invested by a 
sheath of dura prolonged from the margins of the fora- 
mina. The dura mater of the cord does not separate into 
two laters and forms neither sinuses nor processes. It per- 

(1) Dura mater spinalis. 

(2) Plexus venosl vertebrate* lnternl. 



160 THE BRAIN AND SPINAL CORD. 

forms no periosteal function and possesses no Pachionian 
bodies. Its two surfaces are formed by endothelium. 

Arachnoid. — The arachnoid 3 of the spinal cord forms a 
sack of the same length as the dural sheath, with which it is 
externally in contact. It presents two serous surfaces. In- 
ternally, bands of fibro-elastic tissue attach it to the pia 
mater, and form the posterior fenestrated septum. 4 The 
medulli-spinal veins 5 and a considerable space separate the 
arachnoid from the pia mater. That subarachnoid space is 
filled with fluid. By the ligamenta denticulata it is divided 
into the anterior and posterior subarachnoid spaces, 6 which, 
through the foramen magnum, are continuous with the same 
spaces in the cranial cavity. 

Pia Mater. — The pia 7 of the cord is much stronger than 
that of the brain. It has two distinct layers, the inner of 
which is continuous with the brain pia and forms an epi- 
neurium for the cord and roots of the spinal nerves. The 
outer is the more vascular layer. Both layers dip into the 
anterior median fissure; they form the anterior septum 
which contains the anterior spinal artery. Only the inner 
layer is attached to the septum in the posterior median fis- 
sure. The outer layer forms the linea splendens along the 
front of the cord, and the ligamentum denticulatum on 
either side. The denticulate ligament is a longitudinal band 
whose smooth medial border is continuous with the pia along 
the middle of the lateral surface of the cord : its lateral bor- 
der is notched and its twenty teeth, invested with arachnoid, 
are attached to the dura opposite the first twenty vert eb rag. 
The two ligaments subdivide the space between the pia and 

(3) Arachnoidea spinalis. 

(4) Septum subarachnoideale. 

(5) "Venae spinales externa?. 

(6) Cavum subarachnoideale arterius and posterius. 

(7) Pia mater spinalis. 



MEMBRANES OF THE SPINAL CORD. l6l 

arachnoid into anterior and posterior subarachnoid spaces. 
A filamentous extension of the pia below the cord proper 
forms the filum terminale. It descends in the arachno-dural 
sheath with the roots of the lumbar and sacral nerves, and 
all together constitute the cauda equina. For some distance 
the filum terminale contains gray matter and rudimentary 
fibers continuous with the spinal cord. The filum unites 
with the arachnoid and dura at the third sacral vertebra in 
forming the central ligament of the spinal cord. That liga- 
ment is inserted into the coccyx. The pia mater of the cord 
contains the trunks and large branches of the anterior 8 and 
the two posterior spinal arteries, 9 and the tributaries of the 
medulli-spinal veins. 10 The membranes of. the spinal cord 
are supplied by recurrent branches of the spinal nerves and 
by the sympathetic. 

(8) Arteria spinalis anterior. (10) Vense spinales externse. 

(9) Aa. spinales posteriores. 



CHAPTEE IX. 



THE SPINAL CORD. 

The spinal cord 1 is developed from the posterior part of 
the neural tribe, and forms the corresponding portion of the 
central axis of the nervous system. 

Extent. — It is continuous with the medulla oblongata, 
above; and, in the adult, reaches to the lower border of the 
first lumbar vertebra. Its length is seventeen to eighteen 
inches. In a very slender process, the filum terminale, the 
cord is continued beyond the first lumbar vertebra. That 
process and the lower spinal nerves form the cauda equina, 
which is inclosed in a sheath composed of the arachnoid and 
dura mater. The filum terminale, for some distance, con- 
tains a prolongation of the central gray matter and ventricle 
of the cord ; and, also, a few fibers, which suggest the coccy- 
geal nerves of lower animals. 

In the foetus before the third month, the cord and spinal 
canal are of equal length. At birth the cord reaches the 
third lumbar vertebra, and it continues to recede with the 
rapid growth of the vertebra to adult life. 

Size. — The spinal cord is shaped like a cylinder, slightly 
flattened from before backward (dorso-ventrally). Its long- 
est diameter is transverse and measures less than half an 
inch, except in the cervical and lumbar enlargements of the 
cord. In the latter, it equals a half -inch ; and, in the former, 
it slightly exceeds it. The thoracic portion of the cord is 

(1) Medulla spinalis. 



THE SPINAL CORD. 163 

small and nearly cylindrical in shape. Divested of its 
meninges and nerves the spinal cord weighs about one ounce 
and a half avoirdupois. 

The cervical enlargement 2 extends from the medulla ob- 
longata to the second thoracic vertebra. Its greatest diameter 
is on a level with the fifth intervertebral disk. It gives 
origin to the nerves which form the cervical and brachial 
plexuses. 

The lumbar enlargement 3 begins at the tenth thoracic 
vertebra and increases to the twelfth. Opposite the first 
lumbar vertebra, it tapers off almost to a point, the conns 
terminalis, 4 but a very small process continues in the filum 
terminate. From the lumbar enlargement rise the nerves 
forming the lumbar and sacral plexuses. 

Sixth Ventricle. — The central canal 5 of the spinal cord is 
the representative of the cavity of the neural tube. It is 
just visible to the naked eye; but it extends throughout the 
cord and expands above into the fourth ventricle. In the 
filum terminale, it is also dilated, forming the inferior 
rhomboid fossa. 6 It is lined with columnar ciliated cells 
which stand on a thick lamina of substantia gelatinosa 
Eolandi. 

SURFACE. 

Fissures of the Spinal Cord. — The spinal cord is incom- 
pletely divided into symmetrica] lateral halves by the an- 
terior and the posterior median fissure. 

The anterior median fissure 1 is the broader and shallower 
of the two. It extends in length Prom the posterior end of 
the ventral surface of the pons (foramen caecum o( Vicq 
d' Azyr) down the anterior median line of the medulla and 

(2) Intumescentia cervicalis. (5) Canalis centralis spinalis. 

(3) Intumescentia lumballs. (6) Fossa rhomboldea Inferior. 

(4) Conus medullaris. (7) Fissure medlana anterior. 



164 THE BRAIN AND SPINAL CORD. 

cord. As to depth, it equals one-third of the cord's axis. Its 
floor is formed by the anterior, or white, commissure. Both 
layers of pia mater dip down into it and inclose the anterior 
spinal artery and its branches. The anterior median fissure 
is interrupted at the junction of the cord and medulla by 
the decussation of the pyramids. In the lumbar enlarge- 

The posterior median fissure 8 is narrow and deep. It ex- 
tends, longitudinally, down the posterior median line of the 
cord from the middle of the dorsal surface of the medulla. 
It divides the cord, dorso-ventrally, beyond its middle. The 
floor of the fissure is formed by the posterior, or gray, com- 
missure, which, with the white commissure, separates the 
posterior from the anterior median fissure. The posterior 
median fissure is occupied by a lamina of connective tis- 
sue, the posterior septum, which is attached to the deep 
layer of the pia mater. In the posterior septum ramify 
branches of the two posterior spinal arteries and tributaries 
of the medulli-spinal veins. 

Pustero-lateral Fissure. — Each lateral half of the spinal 
cord is partially divided, near the junction of the posterior 
fourth with the anterior three-fourths of its semicircumfer- 
ence, by the postero-lateral fissure. 9 The fissure is situated 
opposite the posterior cornu of gray matter, to which it 
transmits the posterior roots of the spinal nerves. It is con- 
tinuous above with the dorso-lateral groove of the medulla. 
It separates the posterior surface and the antero-lateral sur- 
face from each other. 

Antero-lateral Fissure. — It is convenient to regard the 
narrow longitudinal area, through which issue the anterior 
roots of the spinal nerves, as the antero-lateral fissure. The 
anterior roots do not emerge in line one above another, nor 

(8) Fissura mediana posterior. (9) Sulcus lateralis posterior. 



THE SPINAL CORD. 165 

is there any groove on the surface of the cord, thus the so- 
called fissure cannot be exactly located. It is situated op- 
posite the anterior cornu of gray matter and in line with 
the ventro-lateral groove of the medulla oblongata. It sub- 
divides the antero-lateral surface into anterior and lateral 
surfaces. 

The 'posterior intermediate furrow 10 is a slight longi- 
tudinal groove which subdivides the posterior surface into 
postero-median surface and postero-lateral surface. From it 
a connective tissue septum extends into the cord and sepa- 
rates the columns of Goll and Burdach from each other. The 
posterior intermediate furrow is found only in the upper 
part of the cord, in the cervical and dorsal regions. 

SUBSTANCE OF THE SPINAL CORD. 

The spinal cord is composed of, (1) Gray matter, in the 
central part; and, (2) White matter, in the peripheral area. 
It is like the medulla and pons in having the white matter 
on the surface. 

1. Gray Matter oe the Cord. 

A column of gray matter} 1 crescentric in section, extends 
through the center of each lateral half of the spinal cord. 
The crescent is convex medially; and is joined to its fellow, 
a little in front of the middle, by a transverse lamina of gray 
matter, called the posterior commissure. 12 It is joined to 
the white matter of the opposite side by the anterior com- 
missure. 13 The points of the crescent are directed forward 
and backward, respectively, and form the anterior and pos- 
terior cornua. 14 Together, the two crescents and the gray 

(10) Sulcus intermedius posterior. 

(11) Substantia grisea. 

(12) Commissura posterior et c. anterior grisea 

(13) Commissura anterior alba. 

(14) Columnoe anteriores and c. posteriores. 



l66 THE BRAIN AND SPINAL CORD. 

commissure form an H-shaped column of gray matter. The 

H-shaped column is well marked in the cervical and thoracic 
regions; but, toward the lower end of the cord, the crescents 
become short and thick and the gray column is almost 
cylindrical. 

The gray matter of the cord is of two kinds: (1) The 
substantia gelatinosa Rolandi, which forms (a) a cap for 
the head of the posterior cornu and (b) an envelope for the 
central canal, or ventricle, of the cord. (2) The substantia 
spongiosa. The latter forms all the H-shaped column except 
the tip of the posterior horns and the thick sheath of the 
central canal. Imbedded in the neuroglia, there is a network 
of medullated nerve fibers, running longitudinally, dorso- 
ventrally and transversely, which gives it a spongy appear- 
ance under the microscope. 

Gray Crescent.— It is made up of (1) the anterior 
cornu; 15 (2) the center, 16 which is joined to its fellow of 
the opposite side by the gray commissure; and, (3) the pos- 
terior cornu. 17 There is a lateral projection from the base 
of the anterior cornu in the cervical and upper dorsal region, 
called the lateral horn. 18 The reticula, or processus reti- 
cularis, forms a lateral projection from the base of the pos- 
terior cornu. It is found in the cervical region. 

(1) The Anterior Cornu 15 is short and thick compared 
with the posterior cornu. It is thickest in the cervical and 
lumbar enlargements; in the mid-thoracic region it is more 
slender. It does not reach the surface of the cord as does the 
posterior cornu. It ends in a bulbous, serrated head, which 
points toward the antero-lateral fissure. From it the anterior 

(15) Columna anterior. 

(16) Substantia intermedia grisea. 

(17) Columna posterior. 

(18) Columna lateralis. 



THE SPINAL CORD. l6y 

roots of the spinal nerves rise ; and, together with the an- 
terior root-fibers, it separates from each other the anterior 
and lateral white columns 19 of the cord. 

Cells. — The anterior cornu contains two columns of large 
vesicular cell-bodies, 20 a medial and a lateral column. These 
columns are continuous throughout the cord. Their axones 
compose the greater part of all anterior roots of the spinal 
nerves. From the lateral column, and from a part of the 
medial, the axones enter the spinal nerves of the same side ; 
the remainder pass through the anterior (white) commis- 
sure 21 to the opposite nerves. They are distributed to the 
muscles of the trunk and extremities. Those neurones whose 
centers are in the medial column are believed to innervate 
the dorsal muscles of the trunk. The muscles of the ex- 
tremities are innervated by the dorso-lateral column ; the 
ventral muscles of the trunk, by the ventro-lateral column. 
In the cervical region, the ventro-lateral column gives orisrin 
to the phrenic and spinal accessory nerves (Quain). The 
end tufts of the pyramidal fibers and of the descending 
cerebellar fibers are in relation with the dendrites or bodies 
of the cells of the anterior cornu. Fibers from the pos- 
terior roots of the spinal nerves and from cell-bodies within 
the cord, likewise, terminate in relation with thorn. The 
cells of the anterior cornu are both motor and trophic (?). 

The cells in the anterior cornu are the seat of hemorrhagic 
inflammation and rapidly degenerate in acute anterior polio- 
myelitis: in progressive muscular atrophy and in amyo- 
trophic lateral sclerosis they degenerate slowly. As a resull 
of the first, sudden paralysis occurs. The muscles waste 
away in the second and third because the nerves controlling 

(19) Funiculus anterior and funiculus lateralis. 

(20) Perikaryons. 

(21) Commissura anterior alba. 



105 THE BRAIN AND SPINAL CORD. 

the muscles and their blood supply are gradually destroyed. 
In the last, the muscles are also spastic, because, as we shall 
see farther on, the involvement of the pyramidal tracts cuts 
off cerebral inhibition. 

(2) The Central 22 Part of the Crescent is both afferent 
and efferent. In it are located important reflex centers, such 
as, the Cilio-spinal, Secretory, Vaso-motor, Visceral, Geni- 
tal, etc. In the lumbar enlargement are centers of defeca- 
tion, micturition, erection, ejaculation, parturition; in the 
cervical enlargement the cilio-spinal, cardio-accelerator, etc.. 
are found. The center of the crescent contains three columns 
of cell-bodies. The intermedio-lateral column of large vesic- 
ular cell-bodies, 23 situated near the lateral surface of the 
crescent; the middle column (Waldeyer), deep in the cres- 
cent at the junction of the gray commissure ; and the vesicu- 
lar column of Clark, 24 which is situated near the inner sur- 
face of the base of the posterior cornu. The neurones of 
the central part of the crescent are largely sympathetic ; this 
is especially true of Clark's column and to less extent of the 
intermedio-lateral column. 

The intermedio-lateral column is best marked in the 
thoracic region ; but is also found in the cervical and lumbar 
cord. Its cell-bodies, 23 which are large and vesicular, are in 
relation with end-tufts of fibers from the posterior roots; 
and they give rise to efferent fibers that enter the anterior 
roots of the spinal nerves. Those fibers are probably sympa- 
thetic and supply the muscles of the glandular and circu- 
latory systems (Morris). Other axones from this column 
enter the antero-lateral ascending cerebellar tract. 

(22) Substantia intermedia grisea. 

(23) Perikaryons. 

(24) Nucleus doroalis. 



THE SPINAL CORD. I69 

The middle column (Waldeyer) is composed of medium- 
sized neurone-centers, 23 which are most abundant in the 
cervical region, where this column is best shown. Fibers 
from the posterior spinal roots have been traced into the 
column and probably the cell-bodies give rise to some of the 
fibers of the antero-lateral ascending cerebellar tract, But 
very little is certainly known of the function of this column. 

Clark's column (nucleus dorsalis) is continuous only 
through the thoracic region; but it is represented by the 
nuclei of Stilling, in the cervical and lumbar regions and, 
in the medulla oblongata, by the accessory cuneate nucleus. 
Clark's cells are in relation with the end-tufts of fibers from 
the posterior roots of the spinal nerves. The axones of 
Clark's cells form the direct cerebellar tract, and help to 
form the anterior roots of the spinal nerves. The latter are 
sympathetic fibers, anabolic and inhibitory in function. 
They are distributed to the blood vessels, glands and muscu- 
lar coat of the alimentary canal (Morris). 

(3) The Posterior Cornu, 25 except in the lumbar cord, 
is slender. It is longer than the anterior cornu and roaches 
the surface in the postero-lateral fissure, where it receives 
the posterior roots of the spinal nerves. The posterior cornu 
presents a slight enlargement near its extremity, called the 
caput cornu, 26 which tapers off to the apex cornu. 27 The 
head is joined to the base of the horn by a constricted part, 
the cervix. 28 The head of the posterior horn is capped by 
the substantia cinerea gelatinosa of T?olando. The posterior 
cornu separates the posterior 20 from the lateral column 80 ot 
the cord. 

The cells of the posterior cornu are very numerous. They 

(2F>) Columrin posterior. (?$> Cervix columnse posterioris. 

(26) Caput columns posterioris (29) Funiculus posterior. 

(27) Apex columnse posterioris. (30) Funiculus lateralis. 



170 THE BRAIN AND SPINAL CORD. 

have smaller bodies than the cells of the anterior cornu and 
are less definitely grouped. In function they are afferent and 
associative. They are classified as follows: (a) The periph- 
eral cells, having a body and one long process, the comet cells 
(Waldeyer) ; (b) The central cells; (c) The basal cells; 
(d)" The cells of the substantia gelatinosa, which have small 
and round bodies (Gierke and H. Virchow) ; and (e) The 
solitary, fusiform-bodied cells, scattered throughout the pos- 
terior horn. The dendritic processes of the cells of the pos- 
terior cornu probably ramify in the gray matter adjacent to 
them. The axones run in various directions, viz. : into the 
ground bundles, forming the septomarginal and cornu com- 
missural tracts, and, perhaps the comma tract; into Bur- 
dach's column; into the center and anterior cornu of the 
same side; and, very largely, into the gray crescent of the 
opposite side. These last fibers, together with the antero- 
lateral ascending cerebellar tract, account for the immediate 
crossing of the main sensory path. Many fibers from the 
posterior roots of the spinal nerves terminate in ramifica- 
tions about the cells of the posterior cornu, viz. : Those 
axones, forming the lateral group of small fibers in the pos- 
terior roots of the spinal nerves, end in relation with the 
small, round cell-bodies in the substantia gelatinosa Ro- 
landi; other fibers end about the peripheral, the central, the 
basal and the solitary cell-bodies. 

The Posterior, or Gray, Commissure 31 completes the gray 
matter of the cord. It unites the two gray crescents together 
a little in front of their center, except in the lumbar region 
where it joins their centers. It forms the floor of the pos- 
terior median fissure; and, in front, is in relation with the 
white commissure. It is pierced longitudinally by the cen- 

(31) Commissura anterior grisea, and c. posterior. 



THE SPINAL CORD. I7I 

tral canal of the spinal cord, around which, is a thick en- 
velope of substantia gelatinosa. That part of the commissure 
in front of the canal and that behind it are frequently 
described as the anterior and posterior gray commissures. 
The posterior commissure is composed of neuroglia in which 
are imbedded the bodies of many nerve cells and a large 
number of medullated fibers. The medullated fibers are de- 
rived from the posterior roots of the spinal nerves, and from 
intrinsic neurones of the cord, whose centers are situated 
chiefly in the commissure and in the posterior cornu. The 
commissure contains a long sensory tract between the ven- 
tricle and dorsal surface (Ciaglinski). The long sensory 
tract is found in the thoracic portion of the cord and the 
discoverer believes it to be made up of ascending root-fibers 
which conduct pain and temperature impulses. It is in need 
of further investigation. 

2. White Matter of the Cord. 

The white matter of the spinal 32 cord is disposed in its 
peripheral area and in the anterior commissure. 38 It is com- 
posed of medullated nerve fibers (axones and collaterals) 
imbedded in a small amount of neuroglia; and, like the 
gray matter, it is richly supplied with blood vessels. It is 
also supported by a connective tissue network derived from 
the pia mater. The fibers run transversely, dorso-ventrally 
and longitudinally. 

Transverse fibers are found running between the longi- 
tudinal columns and the gray matter, or vice versa, and are 
continuous with the longitudinal fibers. The most definite 
lamina of transverse 1 libers is the anterior commissure. 

The Anterior, or White, Commissure. -It connects the an- 

(32) Substantia alba. 

(33) Commissura anterior alba. 



172 THE BRAIN AND SPINAL CORD. 

terior and lateral white columns of the cord with the op- 
posite gray crescent. It is located in front of the gray 
commissure, and forms the floor of the anterior median fis- 
sure. It is composed of medullated fibers belonging to the 
direct pyramidal tract, the antero-lateral ground bundle, the 
antero-lateral ascending cerebellar tract, and of the crossed 
fibers to the anterior roots of the spinal nerves. 

The dorso-ventral fibers of the spinal cord are those of 
the anterior roots of the spinal nerves, in their course from 
the gray matter to the surface of the cord; and of the pos- 
terior roots, running from the postero-lateral fissure to their 
destination in the gray matter. 

The longitudinal fibers comprise most of the white matter 
in the cord, forming the funiculus anterior, funiculus later- 
alis and funiculus posterior. They are disposed around the 
gray crescent in bundles or tracts. The tracts are not visible 
to the naked eye, nor under the microscope in a healthy adult 
cord; they have been located by embryological, experimental 
and pathological investigations. The longitudinal fibers rise 
in the brain, in the spinal cord and in the spinal ganglia; 
some run upward and others downward, constituting the 
tracts of the cord. Thus the tracts are characterized as 
ascending, descending and mixed tracts: 

Ascending Tracts: (1) Antero-lateral ascending cere- 
bellar tract, (2) Direct cerebellar tract, (3) Postero-lateral 
tract, (4) Postero-median tract, (5) Marginal tract of Lis- 
sauer, (6) Posterior longitudinal bundle, (7) Olivary bun- 
dle (Helwig^s), and (8) Ciagiinskfs long sensory tract, in 
the gray commissure. 

Descending Tracts: (1) Uncrossed (direct) pyramidal 
tract, (2) Crossed pyramidal tract, (3) Antero-lateral de- 
scending cerebellar tract, (4) Comma tract, (5) Septomar- 



THE SPINAL CORD. 173 

ginal tract, (6) Cornu commissural tract, (7) Anterior 
longitudinal bundle, and (8) Crossed descending tract of 
the red nucleus. 

Mixed, Ascendina and Descending, Tract. — The antero- 
lateral ground bundle. 

The Large Tracts of the Antero-lateral Column 34 of the 
spinal cord are seven in number, viz., the antero-lateral 
ground bundle, two pyramidal tracts, three cerebellar tracts 
and the marginal bundle of Lissauer. 

The antero-lateral ground bundle 35 occupies the deep part 
of the column. It embraces the anterior cornu of gray mat- 
ter and covers the outer surface of the center of the crescent 
and the base of the posterior cornu. It approaches, but does 
not quite reach, the surface of the cord. It is separated from 
the anterior median fissure by the uncrossed (direct) pyra- 
midal tract; the antero-lateral descending and ascending 
cerebellar tracts run between it and the surface of the cord; 
and, behind, it is in relation with the crossed pyramidal 
tract. The antero-lateral ground bundle is composed of as- 
cending and descending fibers. It is a short fiber tract, as- 
sociative and commissural in function. That part situated 
in the anterior column is largely commissural, between the 
anterior cornua; while the part in the lateral column is 
chiefly associative, and connects different segments of the 
cord on the same side. The antero-lateral ground bundle is 
continued in the formatio reticularis of the medulla, pons 
and mid-brain, constituting a short fiber tract which ox- 
tends from the lower part of the cord to the basal ganglia 
of the cerebrum. Some of its ascending fibers form the pos- 
terior longitudinal bundle* 6 and extend up to the motor 

(34) Funiculus anterolateralis. 

(35) Fasciculus proprius anterolateralis. 

(36) Fasciculus longitudinalis medialis. 



174 THE BRAIN AND SPINAL CORD. 

cranial nuclei and hypothalamic region. Imbedded in the 
tract, also, between the anterior and lateral areas, is seen 
the anterior longitudinal oundle B7 throughout the cervical 
region. The latter runs from the anterior quadrigeminal 
body to the cilio-spinal center. 

The uncrossed (direct) pyramidal tract (Turck's column) 38 
occupies a thin area next the anterior median fissure. It is 
a continuation of the same tract in the medulla. Its fibers 
are axones of cortical cells whose bodies are situated in the 
Eolandic region of the cerebrum. As the tract descends in 
the cord, the fibers decussate through the anterior commis- 
sure, and terminate in relation with the cells of the opposite 
anterior cornu. 

The antero-lateral descending cerebellar tract (Loewen- 
thal's column), 39 together with the ascending antero-lateral 
cerebellar tract, occupies a thin peripheral area, broadest pos- 
teriorly, which extends from the direct pyramidal tract out- 
ward and backward, over the antero-lateral ground bundle, 
to the middle of the lateral surface of the cord. Its posterior 
border is in relation with the direct cerebellar tract and the 
crossed pyramidal tract. The fibers of the two tracts are 
mingled together; but the descending fibers are found, 
chiefly, in the anterior part of the common area and the 
ascending in the posterior part. The descending fibers are 
axones from the cortical cells (Purkinje's) of the cerebellum. 
They descend to the spinal cord through the inferior cere- 
bellar peduncle and the lateral area of the medulla and, 
probably, end in the anterior cornu of gray matter. The 
descending cerebellar tract forms one segment of an indirect 
motor path. 

(37) Fasciculus ventralis. 

(38) Fasciculus cerebro-spinalis anterior. 

(39) Fascicularis anterolateralis superficialis (descendens-ascen- 
dens). 



THE SPINAL CORD. 1^5 

Antero-lateral ascending cerebellar tract (Column of 
Gowers). 39 — It is found chiefly in the posterior part of the 
area common to it and the descending tract. It is composed 
of axonic processes of cells whose bodies are situated in the 
center of the crescent and base of the anterior cornu, chiefly 
on the opposite side of the cord. Most of the fibers of the 
antero-lateral ascending cerebellar tract cross near their 
origin through the anterior commissure of the cord. In the 
medulla, the tract ascends through the dorsal part of thp 
lateral area, sending collaterals to the lateral nucleus; it 
then continues, through the formatio reticularis of the pons. 
to a point near the posterior quadrigeminal body, where it is 
bent backward under the superior cerebellar peduncle, and 
enters the vermis cerebelli superior through the valve of 
Vienssens (Hoche). According to Mott. a small bundle 
leaves this tract at the angle, and runs with the lateral filW 
to the posterior corpus quadrigeminum and optic thalamus. 
Gowers' tract carries thermic and pathetic imuulses. The 
olivary bundle of the cord, the triangular tract of TTolwis:. 
is found near the middle of the area common to the antero- 
lateral cerebellar tracts: it may be traced to the lumbar 
region, where its longest fibers rise. Tt ends in the olive of 
the medulla oblongata and is afferent in conduction. 

The direct cerebellar tract (dorso-lateral cerebellar 
tract) 40 runs posterior to the antero-lateral tracts. Tt is 
snperficiallv located, and extends from the middle of the 
lateral surface of the cord back to ilw nostero-lateral fissure, 
except in the lumbar cord. There its absence allow? the 
crossed pyramidal tract to come to the surface. The direct 
cerebellar tract terminate? in ihc superior worm of fhc cere- 
bellum. Tn the medulla, it forms a part of the restiform 

(ifO Fasciculus cerebello-spinalis. 



1/6 THE BRAIN AND SPINAL CORD. 

body. Its fibers are axones of Clark's vesicular cells. They 
convey impulses of equilibrium received, especially, from the 
viscera. 

The crossed pyramidal tract 41 forms a considerable part 
of the lateral column of the spinal cord. It is covered, 
superficially, by the cerebellar tracts in the cervical and 
dorsal cord; but in the lumbar cord, it forms part of the 
surface. Its deep surface is in relation with the posterior 
cornu of gray matter, the antero-lateral ground bundle and 
marginal bundle of Lissauer. The fibers composing it are 
axones of cell-bodies in the Eolandic region of the cerebral 
cortex. They rise with . those of the uncrossed (direct) 
pyramidal tract; 42 and they run as one tract down through 
the genu and anterior two-thirds of the posterior segment of 
the internal capsule, the middle three-fifths of the crusta, the 
ventral longitudinal fibers of the pons and the pyramid of 
the medulla. In the medulla the two tracts separate. The 
crossed tract decussates with its fellow through the anterior 
median fissure, pierces the anterior gray cornu and descends 
in the lateral column of the cord. It terminates in relation 
with the cell-bodies of the anterior cornu. The uncrossed 
tract follows the anterior median fissure as already described. 
Both end chiefly in the anterior gray cornu opposite to their 
cortical origin. According to Marchi, about twenty per cent 
of the fibers remain uncrossed. The pyramidal tracts are 
the cerebral motor tracts. By them motor and inhibitory 
impulses are carried to the cord. In the dorso-lateral part 
of the crossed pyramidal area is found the crossed descending 
tract of the red nucleus. It extends as far as the first lumbar 
segment and ends in the center of the gray crescent. It is 
efferent in function. 

(41) Fasciculus cerebro-spinalis lateralis. 

(42) Fasciculus cerebro-spinalis anterior. 



THE SPINAL CORD. 1 77 

The pyramidal tracts (especially the crossed) are involved 
in lateral sclerosis and in amyotrophic lateral sclerosis; and. 
as a consequence of it, both voluntary and inhibitory im- 
pulses from the brain are interfered with, hence the spastic 
paralysis and exaggerated reflexes. The pyramidal tract may 
be more or less involved in insular sclerosis and in bulbar 
paralysis, and the symptoms vary with the amount of 
sclerosis. Gliosis of the pyramidal and cerebellar tracts and 
the posterior tracts (Dejerine and Letulle) has been demon- 
strated in Friedrich's hereditary ataxia, and the involvement 
of the pyramidal tracts explains the spastic paralysis which 
affects both the arms and legs. In ataxic paraplegia 
(Gowers) there is diffuse sclerosis of the lateral and posterior 
columns of the cord. It is the degeneration in the pyramidal 
tracts that causes the spastic gait, incoordinated arm move- 
ments and early increase of the reflexes, observed in that 
affection. 

The marginal tract of Lissaeur 43 is a small tract com- 
posed of ascending branches of the outer set of fibers in the 
posterior roots of the spinal nerves. It is situated on the 
lateral surface and apex of the posterior cornu. Tts fibers, 
after ascending a short distance, end about the cell-bodies of 
the substantia gelatinosa Rolandi. 

Tracts of the Posterior Column 44 of the Cord. — There are 
three tracts in this column, viz., the postero-lateral, the 
postero-median and the ground bundle, or fasciculus pro- 
prius, which may be divided into the comma tract, septo- 
marginal tract and cornu commissural tract. The lasi three 
are descending tracts. 

Postero-lateral tract (BnrdaeVs column). 46 — Tt runs up- 
ward just medial to the posterior cornu of gray matter. Tt is 

C43) Fasciculus marginalis (45) Fasciculus cuneatus. 

(44) Funiculus posterior. 



178 THE BRAIN AND SPINAL CORD. 

made up of ascending branches of the posterior roots of the 
spinal nerves and of intrinsic fibers whose cell-bodies are in 
the gray matter of the cord. It becomes the fasciculus cunea- 
tus and fasciculus Eolandi, in the medulla; and it ends 
chiefly in the cuneate and Eolandic nuclei. A certain number 
of its fibers are continued directly into the interolivary fillet 
and others into the arciform fibers without interruption ; and 
some of the fibers of Burdach's column end in the gray 
matter of the cord as they ascend. In the midst of the 
postero-lateral tract, in the cervical and upper thoracic cord, 
is a small bundle of descending fibers, the comma tract; in 
the lumbar and sacral segments are found two descending 
tracts, the septomarginal and the cornu commissural. The 
two latter tracts are entirely intrinsic, and there seems to be 
no doubt that the comma tract is in part so, as some of its 
fibers degenerate after section either of the posterior roots of 
the spinal nerves or destruction of the posterior horn of gray 
matter. Burdach's column conveys all kinds of common 
sensory impulses. 

The cornu commissural tract is placed between the pos- 
terior cornu, the gray commissure and posterior septum 
(Gordinier). 

Septo -marginal Tract (Bruce and Muir). — This tract is 
a semi-oval tract next the posterior septum in the third 
lumbar segment (Flechsig) ; and a triangular tract bounded 
by the septum and dorsal surface of the cord in the fifth 
sacral segment (triangle median, Gombault and Phillipe). 

The Comma Tract. — It is comma-shaped in section, the 
head being directed forward. It is composed of descending 
branches of the posterior roots of the spinal nerves, and of 
intrinsic fibers of the spinal cord. It is considerably inter- 
mingled with fibers of the postero-lateral tract, and its 
termination is in the posterior cornu of the cord. 



THE SPINAL CORD. 179 

The posterior median tract (GolPs column) 46 ascends 
between the postero-lateral tract and the posterior median 
septum. Like the postero-lateral tract, it extends in depth 
ventrally to the gray commissure. It is composed of ascend- 
ing branches of the posterior roots of the spinal nerves. 
Continued into the medulla oblongata, the postero-median 
tract becomes the fasciculus gracilis. It terminates at the 
clava, the fibers ending in relation with the cell-bodies of the 
nucleus gracilis. A number of fibers, diverging from the 
tract, end in the gray matter of the spinal cord, and a few, 
without interruption, continue in the interolivary fillet to the 
thalamus and in the arciform fibers of the medulla to the 
cerebellum. GolFs column carries impulses of the muscular 
sense, and is particularly involved in locomotor ataxia. All 
varieties of impulses of bodily sensation are carried by 
Burdach's column. 

Lesions in the posterior columns cause disturbances of 
sensation, loss of reflexes and impaired equilibration. These 
columns are usually involved, by extensions from the poste- 
rior roots, in locomotor ataxia (posterior sclerosis), hence 
the parasthesia, crises, loss of reflexes, contracted pupil, 
disturbed equilibrium and ataxic gait. They may be in- 
volved in insular sclerosis, and the sensory symptoms depend 
upon the extent of their degeneration. Section of the pos- 
terior column on one side in any segment of the spinal cord 
produces, on the same side, more or less loss of sensation in 
that part of the body supplied by the segmeni ml. and, on 
the opposite side, complete anesthesia below the section, 

ROOTS OP THE SPINAL NERVES. 
Thirty-one. pairs of spinal nerves rise from the side of the 
cord. Each nerve has two roots: an anterior, efferenl or 

(46) Fasciculus gracilis. 



180 THE BRAIN AND SPINAL CORD. 

motor, root and a posterior, afferent or sensory, root. These 
roots descend more or less from their origin to the inter- 
vertebral foramen in which they unite to form the spinal 
nerve. The roots of the first cervical nerve are horizontal; 
those of the first dorsal nerve descend the width of two 
vertebras, and those of the twelfth dorsal, the width of four 
vertebrae ; while the roots of the coccygeal nerve extend from 
the first lumbar vertebra to the second piece of the coccyx, 
through ten vertebrae. 

Anterior Root. — In all spinal nerves, except the first, the 
anterior root 47 is smaller than the posterior. 48 It is com- 
posed of from four to six fasciculi, which soon combine into 
two bundles. After piercing the dura mater, the anterior 
root unites with the posterior, beyond the latter' s ganglion, 
and forms a spinal nerve. It is efferent, or motor, in function. 

Superficial (apparent) Origin. — The anterior root is com- 
posed of medullated axones which issue from the narrow 
longitudinal area commonly called the antero-lateral fissure. 

Deep (real) Origin. — The medullated axones rise from the 
medial, lateral, Clark's and intermedio-lateral columns of 
cell-bodies on the same side, and from the medial column of 
the opposite side. 

The lower motor neurones (spinal and cranial) are prob- 
ably in a state of toxic irritation in laryngismus stridulus, 
tetanus, acute ascending paralysis (Landry), strychnine 
poisoning, etc., hence the twitchings, spasms and convulsions. 
In spinal meningitis both the anterior and posterior roots 
are affected. 

The posterior root 49 is the sensory, or afferent, root. It 
is larger than the anterior root, except in the case of the first 
cervical nerve; and is composed of from six to eight fas- 

(47) Radix anterior. (49) Radix posterior. 

(48) Radix posterior. 



THE SPINAL CORD. l8l 

ciculi, which also combine at once into two bundles. The 
posterior root pierces the dura mater separately. It unites 
with the anterior root in the intervertebral foramen. Near 
the outer end, it presents a swelling which contains large 
vesicular bodied nerve cells, and is called a spinal ganglion. 50 
(It is occasionally absent on the first nerve.) The posterior 
root, external to the ganglion, is made up of the dendritic 
processes (Cajal) of the ganglion cells. These dendrites 
extend to the most distant parts of the body; they are the 
sensory fibers of the spinal nerves. Internal to the ganglion, 
the posterior root is composed of axones, which rise from the 
ganglion cells. Both the axonic and dendritic processes are 
medullated. 

Superficial Origin (apparent central termination). — The 
posterior roots of the spinal nerves enter the postero-lateral 
fissure; and, at once, divide into an outer set of small fibers 
and an inner set of large fibers with some small ones inter- 
spersed. The fibers of each set bifurcate into a large 
ascending and a small descending branch. Collaterals rise 
from the main axone and from both branches. 

Deep Origin (real central termination,). — The ascending 
divisions of the outer set of fibers run a short distance along 
the external surface of the posterior cornu, and end in 
ramifications about the cell-bodies of the substantia gelatinosa 
Eolandi. They form the tract of Lissauer. The ascending 
divisions and collaterals of the inner set of fibers from the 
posterior root run (1) to the gray matter of the cord, viz.: 
to all parts of the posterior cornu, to the center of the 
crescent, and to the anterior cornu on the same side. ami. 
through the gray commissure, to the center and anterior 
cornu of the opposite crescent. Those libers end in relation 

(50) Ganglion spinale. 



■I 82 THE BRAIN AND SPINAL|C0RD. 

with the dendrites or cell-bodies situated in those several 
regions. (2) To the brain. Of the ascending fibers from 
the posterior roots of the spinal nerves, the remainder form 
the column of Goll and most of Burdaclr's column and ascend 
to the gracile, cuneate and Rolandic nuclei of the medulla 
oblongata. The greater number terminate in those nuclei, 
but a few continue, through the external arciform fibers, to 
the vermis cerebelli superior, and, through the interolivary 
fillet, to the cerebrum. 

The descending branches of the posterior root-fibers have 
a short course. They end in the gray matter of the cord. 
According to Mott some of them enter into the comma tract. 
They are not well understood. 

The posterior roots of the spinal nerves are first affected 
( Obersteiner and Redlich) in locomotor ataxia, and the lesion 
extends to the spinal ganglia (often) and to the posterior 
columns of the cord. 

BLOOD SUPPLY OP THE SPINAL COED. 

The vessels supplying the cord are the anterior spinal 
artery 51 and the two posterior spinal arteries, 52 which rise 
at the foramen magnum from the vertebral arteries, and are 
reinforced by cervical, intercostal and lumbar arteries. The 
anterior spinal artery descends along the entrance to the 
anterior median fissure; it is formed by the union of two 
vessels, one from each vertebral. The posterior spinal artery, 
of either side, is in reality a pair of vessels which freely 
communicate, and are so placed as to embrace the posterior 
nerve roots. The larger vessel of the pair is external to the 
nerve roots, while the smaller is between them and the pos- 

(51) Arteria spinalis anterior. 

(52) Arterise spinales posteriores. 



THE SPINAL CORD. 183 

terior median fissure. The spinal arteries give origin to two 
sets of branches, namely, the centrifugal and centripetal 
arteries. Both sets are end-arteries and form rich longitu- 
dinal plexuses, which overlap each other but do not 
anastamose. 

The centrifugal arteries rise, first and chiefly, from the 
anterior spinal artery. These enter the anterior median 
fissure and, running lateralward, supply the greater part of 
the gray matter. Second, a few centrifugal arteries rise 
from the posterior spinal arteries. Running into the poste- 
rior fissure, thev are distributed to the posterior white 
columns, the posterior commissure and to Clark's column of 
cells. 

The centripetal arteries rise from both the anterior and 
posterior spinal arteries. Thev enter the cord at ri^ht anq-lpp 
to the surface, and supply the white matter and the peripheral 
parts of the srrav substance, including: the cornua. Those 
branches to the cornua accompany the root-fibers. 

Veins. — The veins 53 that carry the blood from the interior 
of the cord are the fissural veins, which issue from the 
fissures, the root-veins, which accompany the anterior and 
posterior root-fibers to the surface of the cord, and a small 
number of veins that issue from other parts of the surface of 
the spinal cord. All unite in forming the medulli-spindl 
plexus* 4 spread over the entire surface of the cord beneath 
the arachnoid membrane. Tn the upper cervical region, the 
plexus forms two or three small veins which empty into the 
vertebral or inferior cerebellar veins; elsewhere, by a branch 
along each spinal nerve, the plexus communicates with the 

(53) Vense. 

(M) Venae splnalos externae. 



I84 THE BRAIN AND SPINAL CORD. 

meningo-rachidian veins, 55 outside the dura mater, and is 
drained into the vertebral, intercostal, lumbar and sacral 
veins. No valves are found in the spinal veins. 

Lymphatics. — Perivascular and perineural spaces carry 
the lymph from the spinal cord. There are no lymphatic 
vessels in the cord. 

(55) Plexus venosi vertebrates interni. 



CHAPTER X. 

TRACING OF IMPULSES. 

Having studied the grouping and chaining together of 
neurones, let us now make the knowledge practical by tracing 
impulses through the better known paths formed by these 
various neurone groups. The paths thus formed are of three 
kinds, namely: I. Efferent, or motor; II. Afferent, or 
sensory, — General and Special sense; and III. Reflex. 

I. Efferent, or Motor, Paths. 

The Pyramidal Paths are direct, as they do not pass 
through the cerebellum. Their impulses ultimately run 
either through the spinal or the cranial nerves, and are both 
motor and inhibitory. Hence the increased reflexes and 
spastic contractions of lateral sclerosis. 

1. Through the Spinal Nerves. — Starting in the upper 
three-fourths of the Rolandic area of the cerebral cortex, 
motor and inhibitory impulses run down through the 
corona radiata, the anterior two-thirds of the posterior 
segment of the internal capsule, the middle three-fifths of 
the crusta, the ventral longitudinal fibers of the pons, and 
the pyramid of the medulla oblongata, whence they proceed 
either by the crossed or uncrossed (direct) pyramidal tract 
to the anterior gray cornu in the opposite side of the spinal 
cord. By the former route, the impulses cross over in the 
medulla, through the decussation of the pyramids, and de- 
scend in the lateral column of the spinal cord; but by the 
uncrossed route, they descend in the anterior column of the 



1 86 THE BRAIN AND SPINAL CORD. 

cord and decussate, in succession, through the white commis- 
sure. Impulses by either route finally reach the anterior 
gray cornu of the spinal cord and, with the exception of a 
small per cent of them, they reach the cornu opposite to 
their Eolandic origin. The few undecussated fibers in the 
crossed pyramidal tract conduct uncrossed impulses to the 
anterior cornu of the same side. Thus are explained two 
symptoms of hemiplegia, viz., weakness on the well side and 
slight motion on the paralyzed side. From the 'anterior gray 
cornu of the spinal cord the nerve commotions are conducted 
by the efferent, or motor, fibers of the spinal nerves to the 
muscles of the neck, trunk and extremities. 

2. Through the Cranial Nerves. — Impulses destined to the 
cranial nerves run chiefly from the lower two-fourths of the 
Eolandic area through corona radiata, genu of internal cap- 
sule and on, by the same path as the impulses to spinal 
nerves, down to the point where they leave the pyramidal 
tract to enter the nuclei of the cranial nerves, which they do 
in the vicinity of the several nuclei. They enter the nucleus 
of the fourth nerve on the same side, but they cross over to 
the nuclei of the third, fifth, sixth, seventh, ninth, tenth, 
eleventh and twelfth cranial nerves of the opposite side. By 
the above nine nerves innervation is conducted to the muscles 
of the orbit; the muscles of mastication, and expression; 
the muscles of the tongue, palate and ear; the digastric and 
slyloid muscles; the muscles of the larynx, trachea and 
bronchi, and of the pharynx, oesophagus, stomach, and the 
intestines down to the rectum. And inhibitory impulses are 
carried to the heart. 

The Cerebro-corticopontal Paths, Frontal and Tem- 
poral. — These paths are indirect, for spinal nerves, since 
they run through the cerebellum. Frontal. — The impulses 



TRACING OF IMPULSES. 1 87 

originate in the prefrontal region, at the anterior end of the 
superior and at the foot of the middle and of the inferior 
frontal gyri, and descend through corona radiata, the ante- 
rior segment of the internal capsule and the inner (medial) 
fifth of the crusta; or Temporal. — They rise in the temporal 
cortex and ran through corona radiata, the posterior seg- 
ment and inferior lamina of the internal capsule, and the 
outer (lateral) fifth of the crusta. In both paths they run 
to the nucleus pontis' of the same side and to motor nuclei of 
the cranial nerves, whence they proceed to spinal or cranial 
nerves. (1) To spinal nerves they run through the middle 
peduncle of the cerebellum to the cerebellar cortex and, 
thence, continue down ' the antero-lateral descending cere- 
bellar tract to the anterior gray horn of the spinal cord. Their 
course from the cerebellar cortex is through the restiform 
body, the lateral area of the medulla and the antero-lateral 
column of the cord. From the gray matter of the spinal 
cord the impulses are conveyed by the motor fibers of the 
spinal nerves to the muscles which they supply. (2) To 
cranial nerves, the impulses run from the synapses formed in 
the cranial nuclei, by the fibers of the fronto-pontal and 
temporo-pontal tracts, through the motor fibers of the nerves 
to their distribution. 

The Path Through tele Intermediate Bundle of 
the Crusta. — Cortical impulses of unknown origin are re- 
ceived by the corpus striatum and convoyed by a bundle of 
centrifugal axones, which form the deep portion of the 
crusta, to the nucleus pontis, chiefly of the same side. The 
impulses thus traverse the internal capsule and a broad but 
I Inn area in the crusta just ventral io the substantia nigra 
and dorsal Io (ho pyramidal tract. From the nuclei pontis. 
they proceed io the cerebellar cortex by way o\' the middle 



188 THE BRAIN AND SPINAL CORD. 

peduncle of the cerebellum, and may continue down the 
descending cerebellar tract as already given. 

Paths Through the Eed Nucleus. — There are two, a 
direct and an indirect. Impulses run from some part of the 
cerebral cortex to the optic thalamus and red nucleus or to 
the corpus striatum and red nucleus. From the red nucleus 
they pursue either a direct or indirect route. 

(1) Direct Route. — By the direct route, impulses run 
through the crossed descending tract of the red nucleus to 
the center of the gray crescent in the opposite side of 
the spinal cord. Crossing the median raphe at once, in the 
hypothalamic region, the impulses descend by way of the 
above tract through the ventral part of the formatio reticu- 
laris of the mid-brain and pons, in the medial part of the 
lateral fillet, then through the lateral area of the medulla 
among the fibers of the antero-lateral ascending cerebellar 
tract, and finally down the spinal cord, through the dorso- 
lateral portion of the crossed pyramidal area, to their desti- 
nation in the gray matter. From the center of the gray 
crescent they proceed with or without interruption to the 
anterior roots of the spinal nerves, and are conducted to the 
muscles. 

(2) Indirect Route. — Impulses from the red nucleus may 
also run through the superior cerebellar peduncle, chiefly the 
opposite one, to the corpus dentatum, and thence, by axones 
from that nucleus, to the cortex of the cerebellum. The 
descending cerebellar tract continues their path to the 
anterior cornu of the cord. 

Short Fiber Paths. — Those are paths in the formatio 
reticularis chiefly. (1) Impulses having reached the great 
ganglia of the cerebrum and mid-brain may run down the 
formatio reticularis of mid-brain, pons and medulla and the 



TRACING OF IMPULSES. l8g 

antero-lateral ground bundle of the spinal cord to the gray 
crescent of the same, and continue through the anterior root 
fibers to their destination. On the other hand, the impulses, 
leaving formatio reticularis in mid-brain, pons or medulla, 
may enter the nuclei of motor cranial nerves and be con- 
ducted by them to the muscles supplied by cranial nerves. 
(2) The impulses may leave the formatio reticularis in the 
pons, and run to the cerebellar cortex through the middle 
peduncle of the cerebellum. From the cerebellum they may 
follow the ordinary course through the descending cerebellar 
tract to the anterior gray horn of the cord; or (3) Impulses 
having arrived at the cerebellar cortex by way of the superior 
or middle peduncles, may descend through the cerebello- 
olivary tract, in the restiform body, to the opposite inferior 
olive, and be carried on through descending axones of the 
olive, in the antero-lateral ground bundle, to the gray matter 
of the cord (Koelliker). (4) Impulses descend from the 
nucleus of the third cranial nerve by way of certain fibers in 
the posterior longitudinal bundle to the seventh nerve, where 
it enters into the eminentia teres, and through the facial 
nerve innervate the frontalis, pyramidalis nasi, corrugator 
supercilii and orbicularis palpebrarum. Hence these muscles 
are not paralyzed in nuclear facial paralysis. But if the 
lesion be in the eminentia teres or distal to it, then facial 
paralysis is complete. (5) Through certain fibers in the 
posterior longitudinal bundle which rise in the nucleus of 
the sixth cranial nerve and cross to the opposite nucleus of the 
motor oculi, impulses run from the nucleus of the abducent 
through the opposite third nerve to the internal rectus oculi. 
They explain the conjugate deviation observed in lesions 
affecting the nucleus of the sixth nerve. In nuclear lesions 
of the abducent nerve the external rectus of the same eye 



190 THE BRAIN AND SPINAL CORD. 

and the internal rectus of the other eye are paralyzed if the 
nucleus is destroyed and stimulated if the nucleus is only 
irritated. 

II. Afferent, or Sensory, Paths. 
The sensory paths conduct two varieties of impulses, viz., 
General and Special. The impulses originate in the end- 
organs of the cranial and spinal nerves, and by those nerves 
are conveyed to the cerebro-spinal axis through which they 
reach the proper cortical area in the cerebrum. 

1. General Sensation. 

Through Columns of Goll and Burdach. — GolFs col- 
umn is believed to carry impulses of the muscular sense, while 
impulses of all varieties of general sensation are transmitted 
by Burdach 7 s column. Impulses originating in the end 
organs of the spinal nerves traverse the dendrites of the 
spinal ganglion neurones, the cell-bodies in the ganglia 
(Cajal), and then the axones of the same. They enter the 
cord through the posterior roots of the spinal nerves, and 
ascend through the tracts of Burdach and Goll, in the pos- 
terior column of the cord, to the nuclei of that column in 
the medulla oblongata, chiefly the nucleus gracilis and 
nucleus cuneatus. Thence the impulses may proceed either 
by a direct or by an indirect route. 

(1) The Direct Route carries the impulses by way of the 
interolivary and medial fillet, through the sensory decussation 
of the medulla, the formatio reticularis of pons and mid-brain 
and the crusta of the mid-brain, to the ventro-lateral nucleus 
of the optic thalamus, from which they are conducted by the 
three systems of Flechsig, — namely, the anterior stalk of the 
thalamus, the ansa peduncularis and the ansa lentieularis, — ■ 
to the somaesthetic area of the cerebral cortex. In their last 



TRACING OF IMPULSES. ICH 

stage the impulses run from the optic thalamus through the 
internal capsule and corona radiata to the equatorial zone of 
the hemisphere. 

(2) Indirect Route. — By that route impulses from the 
nucleus gracilis and nucleus cuneatus run to the cortex of 
the vermis cerebelli superior through the external arciform 
fibers; then on, through the superior peduncle of the cere- 
bellum, to the red nucleus and optic thalamus. They 
traverse the restiform body of the same side, by way of the 
posterior external arciform fibers: or, by way of the anterior 
external arciform fibers, they traverse the sensory decussa- 
tion of the medulla and the opposite restiform body to reach 
the vermis cerebelli superior. From the cerebellar cortex, 
the impulses continue through cortical axones to the corpus 
dentatum, whose axones conduct them to the red nucleus and 
optic thalamus of the opposite side. The greater number, 
therefore, cross over in the tegmentum of the mid-brain. 
Their course from the red nucleus and optic thalamus is 
through the three systems of Flechsig to the cortex. 

Through Cranial Nerves and Medtal Fillet. — As 
crossed fibers from the terminal nuclei of the trifacial, the 
vestibular, the glossopharyngeal and the pneumogastric 
nerves join the medial fillet and run to the optic thalamus, 
so impulses of common sensation, transmitted by those cra- 
nial nerves to the medulla and pons, are carried by the medial 
fillet to the ventro-lateral nucleus of the thalamus on the 
opposite side. The systems of Fldchsig, chiefly the ansa 
peduncularis, conduct them to the lower portion of fche 
som aesthetic area. 

Through Direct Cerebellar Tract. — Clark's column of 
cell-bodies in the spinal cord receives impulses concerning 
equilibrium from the posterior roots of the spinal nerves and 



192 THE BRAIN AND SPINAL CORD. 

transmits them at once to the direct cerebellar tract through 
which they ascend along the dorso-lateral surface of the cord, 
along the posterior surface and through the restiform body 
of the medulla to the cortex of the superior worm of the 
cerebellum. To a small extent they cross in the worm to the 
opposite side. From the cerebellar cortex the journey is 
completed in four stages, as already described, namely: 
corpus dentatum, opposite red nucleus, optic thalamus and 
cerebral cortex. 

Through Antero - lateral Ascending Cerebellar 
Tract. — Pathetic and thermic impulses are conveyed by this 
tract. Those impulses enter the center of the gray crescent 
of the cord, partly on the same side, through the posterior 
nerve roots and Burdach's column. A large number decus- 
sate in the above cerebellar tract, crossing in the anterior 
commissure, and run upward through the antero-lateral 
ascending cerebellar tract of the opposite side to the cortex 
of the superior worm of the cerebellum and to the optic 
thalamus. In the cord they ascend along the ventro-lateral 
surface. They run dorsal to the olive in the lateral area of 
the medulla oblongata, and through the lateral part of the 
formatio reticularis of the pons to the angle in Gower's 
tract. From the angle, just behind the quadrigeminal 
bodies, the greater number of impulses run backward with 
the tract through the valve of Vieussens to the cortex of the 
vermis cerebelli superior; the remainder run forward to the 
optic thalamus, and from that to the parietal cortex. The 
common course of sensory impulses from the cerebellar to 
the cerebral cortex is, as already described, through corpus 
dentatum and superior peduncle to opposite red nucleus and 
optic thalamus, though they may run through the middle 
cerebellar peduncle to the pons and then, by way of the 



TRACING OF IMPULSES. 193 

formatio reticularis, the medial fillet, or the posterior longi- 
tudinal bundle, ascend to the optic thalamus. Having ar- 
rived in the thalamus, they proceed thence by the three 
systems of Flechsig to the somaesthetic cortex. 

The Short Fiber Paths. — '(1) The anterolateral ground 
bundle and formatio reticularis contain ascending axones 
which may convey sensory impulses from the gray matter of 
the cord, received from the posterior roots of the spinal 
nerves, or from terminal nuclei in medulla and pons which 
receive the common sensory fibers of cranial nerves, upward 
to the optic thalamus of the opposite side. The course from 
the thalamus by way of the cortical fillet is now familiar. 

(2) Again, impulses may leave the formatio reticularis in 
the pons and run through the middle cerebellar peduncle, by 
way of axones from the nuclei pontis, to the cortex of the 
cerebellum; and then continue by the ordinary course 
through the superior peduncle to the red nucleus and optic 
thalamus. 

(3) Certain fibers of the antero-lateral ascending cere- 
bellar tract divulge from the others, in the medulla oblongata. 
and terminate in the lateral nucleus. Impulses of pain and 
temperature, following the same course, enter the lateral 
nucleus; and are carried on through the restiform body to 
the cerebellum by the tract from the lateral nucleus io the 
cerebellar cortex, thence to the somaesthetic area as previously 
given. 

Destruction of any of the above sensory paths causes loss 
of the especial variety of impulse which travels thai path. 
Destruction of Gpll's column produces loss of muscular sen 
sations, and cases are on record in which a cord lesion 
abolished pain and temperature sensations while touch was 
not affected. 



194 the brain and spinal cord. 

2. Special Sensations. 

Impulses producing the sensations of smell, sight, hearing 
and taste are carried from the respective organs of sense to 
the brain by the following nerves : the Olfactory ; the Optic ; 
the Auditory; and the Glossopharyngeal, cord tympani and 
pars intermedia. 

Olfactory Path. — Impulses of smell originate in the 
upper third of the Schneiderian membrane. They run 
through the olfactory nerves to the second layer in the bulb, 
where they are transferred to the dendrites of the mitral 
cells. By the axones of the mitral cells they are carried 
backward through the olfactory tract and roots to the cere- 
bral hemisphere. The internal, or medial, root conducts 
them to the area of Broca and anterior end of the gyrus f orni- 
catus, whence through the cingulum and uncinate fasciculus 
they reach the cortical area of smell in the uncus hippocampi. 
By the middle olfactory root the impulses enter the trigone 
and complete their journey either in the same manner as 
given above or via the anterior commissure.' The external, 
or lateral, root of the olfactory tract conducts the impulses 
directly to the uncus of the hippocampal convolution. Note 
that olfactory impulses are chiefly, if not entirety, uncrossed. 

Optic Path. — Impulses of sight originate in the rods and 
cones of the retinae and traverse three or more series of 
neurones to the terminal nuclei of the optic tracts ; namely, 
the rod and cone, the bipolar and the ganglionar neurones. 
The axones of the last form the optic nerves and the visual 
part of the optic tracts. From the right halves of both 
retinae and from the left halves of both, impulses run 
through the corresponding tract to the external geniculate 
body and the pulvinar of the optic thalamus; also to the 
anterior quadrigeminal body and the nucleus of the motor 



TRACING OF IMPULSES. I95 

oculi nerve. The two latter produce ocular and pupilary 
reflexes. From the lateral geniculate body and pulvinar the 
optic radiations^ carry the impulses through the posterior seg- 
ment of the internal capsule to the half-visual center in the 
cuneus and (to a small extent) the convex part of the 
occipital lobe. Impulses from the nasal halves of the retinas 
decussate in the optic commissure; those from the temporal 
halves, for the most part at least, remain on the same side, 
but a few may cross through the quadrigeminal bodies and 
anterior brachia. 

Auditory Paths. — There are two auditory paths, the 
Cochlear and the Vestibular. The former is concerned with 
hearing and the latter with equilibrium. 

1. The Cochlear Path. — Impulses of hearing originate 
chiefly in the organ of Corti. They are transmitted by the 
rods and hair cells of Corti to the dendrites of the spiral 
ganglion. Traversing the dendrites and cell-bodies of that 
ganglion, they enter the axones, which form the cochlear 
nerve, and run backward to the terminal nucleus of that 
nerve in the medulla. Both the ventral and the dorsal, or 
lateral, portions of the cochlear nucleus (ventral auditory 
nucleus) receive the impulses of hearing. From the cochlear 
nucleus they run either lateral and dorsal to the restiform 
body and cross to the opposite side through the acustic 
strias and trapezium, or they run medial to tin 1 restiform 
body and enter at once into the trapezium. By either course 
they reach the lateral fillet, and chiefly the opposite one. 
The lateral fillets conduct the impulses to the posterior 
quadrigeminal bodies; the posterior brachia to the internal 
geniculate bodies, and the acustic radiations to the third and 
fourth fifths of the superior temporal ami the transverse 
t< mporal gyri of both sides. 



IQ6 THE BRaIN and spinal cord. 

2. Vestibular Path. — The extent of the vestibular conduc- 
tion path is from the acustic areas of the utricle and semi- 
circular canals (and possibly from the saccule) to the 
vestibular nuclei in the floor of the fourth ventricle and, 
thence, to the cerebellum and the cortical area of equilibrium 
in the parietal cortex. It is the path of the space sense. 
Through the vestibular nerve the impulses reach the dor so- 
medial, dorso-lateral and superior auditory (vestibular) 
nuclei in the floor of the fourth ventricle and the spinal 
nucleus, which has not been definitely located, and they 
probably reach the nuclei in the cerebellum also. The im- 
pulses may pursue, from the terminal nuclei in the ventricular 
floor, either a direct or an indirect course to the cerebral 
cortex. 

(1) By the direct course they run through the opposite 
medial fillet and certain fibers in the three systems of 
Flechsig(P). 

(2) The impulses run to the cerebellum, by the indirect 
course, through the acustico-cerebellar tract, and probably 
through uninterrupted fibers of the vestibular nerve in the 
restiform body. They thus reach the opposite nucleus 
fastigii and nucleus giobosus; perhaps a number also reach 
the corpus dentatum and cerebellar cortex. From the cere- 
bellum the course of the impulses is, presumably, through 
the superior peduncle to the red nucleus and optic thalamus 
of both sides and thence to the cortex. They may excite in 
the cerebellum impulses of equilibration which descend to 
the motor nuclei of spinal nerves in the anterior horns of gray 
matter by way of the antero-lateral descending cerebellar 
tracts. 

Impulses, believed to be concerned with reflexes run from 
the vestibular nuclei in the floor of the fourth ventricle (a) 



TRACING OF IMPULSES. I97 

to opposite nuclei of motor cranial nerves via the medial 

fillet; (b) to the quadrigeminal bodies through the superior 
and lateral fillets; and (c) to the inferior olive and lateral 
column of the spinal cord by way of the vestibulo-olivary and 
vestibulo-spinal fibers. 

The Gustatory Paths. — They extend from the tongue to 
the glossopharyngeal muscles in the medulla and thence 
through the opposite medial fillet and inferior lamina of the 
internal capsule to the taste area in the gyrus hippocampi. 
There are two paths from the tongue to the ninth nucleus. 
Those impulses from the base of the tongue and the palate 
run through the ninth nerve and those from the anterior 
two-thirds of the tongue through the corda tympani and pars 
intermedia to the medulla (A. F. Dixon) (see note). 
Possibly, gustatory impulses originating in the palate may 
traverse the descending branches of Meckel's ganglion and 
the great superficial petrosal nerve to reach the geniculate 
ganglion on the facial; and, then, continue through the pais 
intermedia to the glossopharyngeal nucleus. All impulses 
arriving at this nucleus complete their journey in two stages : 
first, through the medial fillet to the opposite thalamus; 
and, second, through internal capsule to the hippocampal 
cortex. 

Destruction of the olfactory conduction path on one side 
causes anosmia on the same side; of the optic tract or radia- 
tions, hemianopia in the corresponding halves of both 
retinae; of the auditory path above the pons, deafness chiefly 
on (he opposite side; and interruption of the gustatory path 
above the medulla oblongata abolishes taste on the opposite( ?) 
side. 



Note.— Edingb. M. J., 1S97, Vol. I, p.395, A. P. Dixon. 

Amer. J. Med. Science, 189S. Vol. E,pp. 502-582, Cases VI and 
VII, Keen and Spiller. 



I98 THE BRAIN AND SPINAL CORD. 

II. Reflex Paths. 

There is no visible limit to the number of reflex paths. 
Hence no attempt will be made to give them completely, but 
a few examples of various kinds will be given which may 
assist the student to trace others and be suggestive of their 
great multiplicity and importance. 

Keflex arcs are formed (1) by the sensory and motor fibers 
of spinal nerves, associated in the gray matter of the cord; 
(2) by the sensory and motor fibers of cranial nerves, which 
are connected in the brain; (3) by afferent spinal fibers, the 
posterior longitudinal bundle, chiefly, and efferent, cranial 
fibers; and (4) by afferent cranial and efferent spinal nerve 
fibers, the two being associated by the anterior longitudinal 
bundle, the spinal root of the fifth nerve, the vestibulo- 
olivary and vestibulo-spinal tracts, the solitary bundle, etc. 

(1) Spinal Keflexes. — In the simplest spinal reflexes, 
the afferent fibers of the arc arborize about the cell-bodies 
whose axones constitute the efferent fibers. Among them are 
the skin and muscle reflexes, such as the plantar reflex, the 
gluteal reflex, the cremaster reflex, the involuntary with- 
drawing of a part from a source of irritation, etc. 

More complicated spinal reflexes are those of defecation, 
micturition, parturition, vasomotor reflexes, cardio-accelera- 
tor reflexes, etc. The impulses traverse at least three 
neurones in these reflexes. As an example, trace a defecation 
reflex. 

Defecation Reflex. — The rectum is supplied by the third 
and fourth sacral nerves and by branches of the inferior 
mesenteric and hypogastric plexuses. Irritation of the sen- 
sory endings in the mucous membrane is caused, normally, by 
the presence of feces. The impulses caused thereby run to 
the special defecation center in the lumbar enlargement of the 



TRACING OF IMPULSES. I99 

spinal cord, either by way of the sacral nerves or through 
the sympathetic plexuses, the ganglionated cord, and the 
rami communicantes to the lumbar nerves, through the pos- 
terior roots of which they reach the center in the cord. From 
the defecation center the impulses pursue two courses: (a) 
They descend through the third and fourth sacral nerves 
and cause inhibition in the circular fibers of the rectum and 
contraction of the longitudinal muscle, (b) This action is 
immediately followed by impulses which pursue the sympa- 
thetic course, through the anterior roots of the lumbar nerves, 
the rami communicantes, the ganglionated cord, and the 
inferior mesenteric and hypogastric plexuses, to the rectum. 
They cause, in succession from above downward, contraction 
of the circular muscle of the rectum. The two series of 
impulses thus open a way for the passage of fecal matter; 
and, then, force it through the opening unless prevented by 
the voluntary contraction of the external sphincter. 

(2) Cranial Reflexes. — The simplest of these reflexes 
are such as spasm of the muscles of mastication caused by a 
bad tooth, in which both limbs of the arc are formed by the 
trifacial nerve. Again, the facial expression of pain due to 
the same cause. In this the impulses traverse the trifacial 
nerve and by the collaterals of its root-fibers reach the 
nucleus of the facial. Through the facial they cause con- 
traction of certain muscles of expression. 

Salivary reflexes, in which the sight of a fine dinner or 
the smell of it, causes the flow of saliva : coughing, sneezing. 
vomiting reflexes and deglutition reflexes are more compli- 
cated, but, knowing the nerve supply of the parts involved, 
the student can trace the impulses. 

(3) Sptnal and Cranial Reflexes.- Impulses received 
by the spinal cord through the afferent fibers of its nerves 



200 THE BRAIN AND SPINAL CORD. 

are transmitted by the posterior longitudinal bundle to the 
nuclei of motor cranial nerves, or, perhaps, through Burdach's 
column and the interolivary fillet to the same nuclei. Thus 
is brought about the movement of the eyes toward the source 
of impulse, a change of facial expression to agree with the 
painful or pleasing character of the impulses, etc. 

(4) Cranial and Spinal Eeflexes. — Of these there are 
many. Let us notice three. 

Respiratory Reflex. — Any obstruction or irritation in the 
larynx or trachea sends an impulse through the pneumo- 
gastric nerve to its sensory nucleus and, through its descend- 
ing branches, in the solitary bundle, to the nucleus ambiguus 
and nucleus of the phrenic nerve in the cervical cord, causing 
increased respiratory effort, coughing, spasm of muscles 
closing the glottis. 

Auditory Reflex. — Turning of the head upon hearing a 
sound, and the sudden starting, caused by hearing a loud 
sound, are illustrations of this reflex. The path for the 
latter is probably as follows: the auditory nerve, the 
vestibulo-olivary and vestibulo-spinal tracts, antero-lateral 
ground bundle and efferent fibers of spinal nerves. 

Pupillary Reflexes. — Pupillary reflexes belong to the cra- 
nial and cranio-spinal group of reflexes. The cilio-spinal 
centers are in the cervical enlargement of the spinal cord, the 
pupillo-dilator in the upper and the pupillo-constrictor in the 
middle part of that enlargement. They receive optic im- 
pulses through the anterior (or ventral) longitudinal bundle 
from the corpora quadrigemina anteriora. The anterior 
quadrigeminal bodies receive those impulses by two routes: 
first, directly, through the fibers of the external root of the 
optic tract, and, second, indirectly, through centrifugal fibers 
in the optic radiations, and the anterior brachium. By the 



TRACING OF IMPULSES. 201 

latter route, the optic impulses which have reached the visual 
area of the occipital lobe, by way of the intrinsic retinal 
neurones and the optic nerves, tracts and radiations, are 
returned to the optic thalamus and external geniculate body 
and then carried back to the anterior quadrigeminal bodies. 
Thence, reaching the cilio-spinal centers through the anterior 
longitudinal bundle, the impulses take one of two courses: 
(a) They leave the spinal cord through the anterior roots of 
the upper thoracic nerves and run, in succession, through the 
rami communicantes, the cervical cord of the sympathetic, 
the cavernous plexus, the ciliary ganglion and the short 
ciliary nerves to the radiating fibers of the iris, causing 
dilation of the pupil, (b) From the pupillo-constrictor 
center, the impulses are carried upward by the posterior 
longitudinal bundle to the nuclei of the motor oculi nerve, 
where they are reinforced by optic impulses received directly 
through the anterior quadrigeminal body and posterior com- 
missure. The impulses reach the ciliary muscle and the 
circular muscle of the iris through the motor oculi, ciliary 
ganglion and short ciliary nerves. The results are contrac- 
tion of the pupil and accommodation for distance. 



CHAPTER XI. 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 

The brain and spinal cord are developed from the neural 
tube; the spinal and sympathetic ganglia and the ganglia of 
sensory cranial nerves are derivatives of the neural crest. 

Yery soon after conception there appears along the median 
line, in the back of the embryo, a plate of epiblast, called the 
medullary plate. That plate soon presents two longitudinal 
elevations, the medullary ridges, separated by a median fur- 
row, the neural groove. The rapid growth and infolding of 
the medullary ridges roofs over and closes in the neural 
groove and thus forms the neural tube. That approximation 
of the medullary ridges produces a slight median elevation, 
which is the neural crest. By the fifteenth day after concep- 
tion the neural tube and crest are complete, except posteriorly, 
where the neural groove is still open. 

Meninges. — Later the neural tube becomes surrounded by 
mesoblast which forms the pia mater, arachnoid and dura 
mater. 

The ITeural Crest. — (1) The cephalic portion of the neural 
crest becomes broken into five pairs of ganglia, which, during 
development, shift their positions to the ventral side of the 
brain. Those ganglia are called the jugular, petrosal, genic- 
ulate, auditory and Gasserian. They give origin to the 
sensory parts of the pneumogastric, glossopharyngeal and 
facia! nerves ; all of the auditory nerve, and the sensory pait 
of the trifacial. In all of the ganglia, except the auditory, 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 203 

the cells develop into unipolar neurones ; they remain bipolar 
in the auditory ganglion. The single processes of the uni- 
polar neurones immediately divide, T-like, into peripheral 
and central fibers, which in appearance are axones. The 
peripheral fibers form the sensory part of the respective 
nerves and conduct impulses toward the cell-body, hence they 
may be considered dendrites (Cajal) ; the central fibers, the 
axones proper, form the part of the sensory nerve between 
the ganglion and the brain. From the auditory ganglion, 
which moves backward to a point behind the geniculate 
ganglion, the dendrites run outward to the acustic areas of 
the internal ear; the axones enter the medulla oblongata. 
All the central axones of the several ganglia divide, T-like, 
upon entering the brain, and collaterals rise from the un- 
divided fibers and from both branches of them. These 
axones and collaterals arborize, chiefly, in the terminal nuclei 
of the respective nerves; but certain of them, the excito- 
reflex fibers, terminate in nuclei of motor nerves. 

(2) The spinal portion of the neural crest forms the 
thirty-one pairs of spinal ganglia situated on the posterior 
nerve-roots; and, also, the vertebral, prevertebral and termi- 
nal ganglia of the sympathetic system. The sympathetic 
ganglia wander widely. In them the epiblastic cells develop 
into multipolar neurones, the nonmedullated processes of 
which constitute the larger number of gray fibers in the 
sympathetic system. The cells of the spinal ganglia form 
unipolar neurones, like those of the jugular, petrosal, genicu- 
late and Gasserian ganglia. Like them, also, the single 
processes divide, T-like, the peripheral arms of (ho T-branches 
forming the sensory part ol' each spinal nerve ami the central 
arms (the axones) the posterior roots of those nerves. The 
latter enter the cord at the posterolateral fissure ami. before 



204 THE BRAIN AND SPINAL CORD. 

and after dividing T-like into an ascending and a descending 
branch, give off collaterals. The descending fibers (axones 
and collaterals) arborize in the gray matter of the cord; the 
ascending terminate chiefly in the spinal cord, and in the 
nuclei of its posterior columns, namely, the nucleus gracilis 
and nucleus cuneatus. A few ascending fibers end in the 
cerebellum and cerebrum. 

The Neural Tube. — It is well formed at the fifteenth day. 
The cephalic, or closed, end of the tube is much larger than 
the caudal end, and presents at this time two constrictions 
that separate the primary brain vesicles from one another — 
the anterior, the middle and the posterior. Behind the 
posterior primary vesicle, the neural tube remains small and 
of nearly uniform size; that part forms the spinal cord. 

The neural tube, up to the fourth week, is composed of a 
single layer of long columnar cells whose ends form the 
exterior and interior surfaces of the tube. The cells contain 
a nucleus in their middle third and present a central and a 
peripheral clear zone. In the central clear zone, near the 
interior surface of the tube, there may be observed between 
the fourth and the fifth week a number of small, round, 
nucleated cells, the nuclei of which are in all stages of 
karyokinesis. These are the germinating cells (His). Soon 
they become elongated and send out a protoplasmic process 
from what was originally (i. e., before the formation of the 
neural tube) the deep, or proximal, end of the cell. Now 
they are neuroblasts, because they are the parents of the 
neurones. The protoplasmic processes form the axones, and 
other processes may or may not develop. Both the axones 
and dendrites grow in the direction of least resistance (His). 
While the neuroblasts are * developing, the columnar cells of 
the neural tube undergo great changes. They become more 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 205 

and more elongated and, by a process of vacuolation, their 
protoplasm becomes perforated and branched and so broken 
up as to entirely destroy the original outlines of the cells. 
The branches appear to unite and form a sort of radial 
net-work in the peripheral clear zone, called the myelospon- 
gium. The elements of the myelospongium are the spongio- 
blasts; they form the neuroglia. At this time the three 
histologic layers begin to show, namely, (1) the outer layer 
(neuroglia), (2) the middle, or mantle, layer, composed of 
neuroblasts, and (3) the inner, or ependymal, layer; also at 
this time a lateral longitudinal groove appears, which extends 
from the mesencephalon to the caudal end of the tube. The 
groove is on the ventricular surface. It gives the lumen of 
the tube a diamond shape, on section, and separates the 
ventral from the dorsal zone. The ventral zone is motor 
and the dorsal is sensory. 

BRAIN. 

The brain vesicles grow rapidly. By the end of the fourth 
week a constriction is visible in the anterior primary vesicle 
and another in the posterior primary vesicle, dividing each 
into two and making in all five secondary brain vesicles, 
which freely communicate with one another and are numbered 
from before backward. They are: 

1. Prosencephalon, or telencephalon. 

2. Thalamencephalon, or diencephalon. 

3. Mesencephalon. 

4. Epencephalon. 

5. Metencephalon, or myelencephalon. 

These vesicles form the brain, their cavities become the 
ventricles. The neuroblasts of the mantle layer produce 
the neurones, whose cell-bodies and dendrites are found 
in the cortex and ganglia, and whose medullated axones 



206 THE BRAIN AND SPINAL CORD. 

form the white substance. The supporting neuroglia is 
formed by the spongioblasts of the neurogliar and ependymal 
layers. 

Flexures. — The cephalic portion of the neural tube is the 
seat of three flexures, two ventral and one dorsal. (1) The 
mesencephalic flexure (ventral) begins very early and 
amounts to nearly 180 degrees by the twenty-eighth day. It 
bends ventrally the thalamencephalon until it almost touches 
the epencephalon. Thus the interbrain and pons are ap- 
proximated. (2) The cervical flexure is also a ventral one. 
It is located at the junction of the fifth vesicle with the 
spinal cord, and corresponds to the bending of the head upon 
the body of the embryo. This flexion begins about the 
twenty-first day. By the end of the fourth week, it is com- 
pleted and amounts to 90 degrees. (3) The dorsal flexure 
is beginning to form at the same time (fourth week). It 
occurs between the fourth and fifth brain vesicles, and is often 
called the metencephalic flexure. It reaches 180 degrees by 
the eighth week, when the dorsal part of the epencephalon 
(the cerebellum) rests upon the metencephalon (the medulla 
oblongata). The cervical and metencephalic flexures almost 
entirely disappear, but the mesencephalic flexure is permanent. 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 



207 



TABLE III. 



BRAIN VESICLES AND THEIR DERIVATIVES. 



Primary Vesicles. Secondary Vesicles. 



Anterior 

(Fore-brain) 



1st. The Prosenceph- 
alon. 



2d. The Thalamen- < 
cephalon. 



Derivatives and Ven- 
tricles. 

Hemispheres and An- 
terior wall of third 
ventricle. (Fora- 
mina of Monro, 
lateral ventricles, 
hemispheres, cor- 
pora striata, olfac- 
tory lobes, fornix, 
anterior commis- 
sure, corpus cal- 
losum and lamina 
terminalis.) 

Inter-brain and 
third ventricle, ex- 
cept anterior wall. 
(Optic thalami, ex- 
ternal geniculate 
bodies, posterior 
and middle com- 
missures, p i n e al 
body, roof epithe- 
lium of third ven- 
tricle and the third 
ventricle, corpora 
albicantia, tuber 
cinereum and In- 
fundibulum. lami- 
na cinerea, retinas, 
optic nerves, 
chiasm and 
tracts.) 



Middle 

(Mid-brain). 



$3d. The Mesencepha- 
( Ion. 



Mid-brain and Aque- 
duct of Sylvius. 
(Orustn?. substan- 
tia nlsra. tesnmen- 
tum. Sylvian aque- 
duct, corpora quad- 
ris:omiua. and in- 
ternal srenlculnte 
bodies.) 



208 THE BRAIN AND SPINAL CORD. 



Posterior 

(Hind-brain). 



* v he Epencepha - ! H p- r -i oLll g 

r+i, rpi,^ tvt«+«««««^o ( After-brain. (The? 
BtkThe Metencepha- oblonga- g 

lon - ( ta.) 9 

The cerebrum is developed from the anterior primary 

brain vesicle as is shown in the outline, being the more 

immediate descendant of the prosencephalon and thalamen- 

cephalon. 

PROSENCEPHALON. 

It is at first a single vesicle forming the fore part of the 
anterior primary vesicle. The median portion of its anterior 
wall (lamina terminalis) remains almost stationary; later- 
ally, it is the seat of rapid growth and produces on either 
side a hollow diverticulum, whose cavity is the primitive 
lateral ventricle and whose walls form the substance of the 
hemisphere. The outgrowth is called the hemisphere vesicle, 
its constricted stalk contains the primitive foramen of Monro. 
The vesicles grow forward and outward at first, separated 
from one another by mesoblast which forms the falx. Later, 
growth occurs in succession, upward, backward and down- 
ward, until by the seventh month the hemisphere overhangs 
every other part of the brain. 

Olfactory Lobe. — In the fifth week a hollow diverticulum 
grows out from the anteroinferior wall of the hemisphere 
vesicle and forms a prominent lobe. It preserves a lobular 
form in the horse, and in some other animals; but in man 
it soon becomes constructed by the fissura prima into an 
anterior and a posterior lobule, and loses its ventricular 
cavity. The anterior olfactory lobule develops the olfactory 
bulb, tract, trigone, and the area of Broca; the posterior 
lobule forms the anterior perforated lamina. 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 209 

Primary Sulci. — The vesicle walls are of uniform thinness 
tip to the second month, being composed of a single layer of 
columnar cells. During their rapid growth in the second 
and third months they become thrown into folds which en- 
croach upon the cavity and present on the surface of the 
vesicle (or hemisphere) the primary sulci. The cause of the 
infoldings is, perhaps, the resistance of the slower growing 
cranium. The primary sulci are best developed in the third 
month. Their location nearly corresponds to the following 
permanent fissures: Sylvian, Parieto-oecipital, Calcarine, 
Hippocampal, Collateral and Anterior Great Transverse 
(choroid) fissure. The hippocampal fissure is the inferior 
part of the Fissura Prima. The superior' part of the latter 
corresponds to the fissure of the corpus callosum, and the 
anterior, which is transverse, separates the olfactory trigone 
from the anterior perforated space. For the most part the 
primary sulci have disappeared by the first of the fifth month 
(at this stage the cranium grows more rapidly than the brain 
vesicles) ; but the ventricular eminences produced by the 
sulci are permanent, namely, the hippocampus major and 
minor and eminentia collaterals. Possibly the caudate 
nucleus belongs in the same group. 

Permanent Fissures. — In the sixth month the primary 
sulci are replaced by the important permanent fissure?, which 
divide the hemisphere into lobes. Many of the smaller per- 
manent sulci appear after birth. The permanent fissures, or 
sulci, are the result of depressions in the surface; they do 
not involve the whole thickness of the ventricular wall. Their 
object is probably to preserve a certain ratio between the cortex 
and the white matter in the hemisphere. ("For the permanent 
fissures, see Exterior Surface of the Cerebrum.) Two of 
the permanent fissures are peculiar, namely: 



210 THE BRAIN AND SPINAL CORD. 

(1) The fissure of Sylvius is formed by the approximation 
of the anterior and posterior walls of the broad Sylvian 
valley, or primary sulcus., in the ventral border of the hemi- 
sphere. The bottom of the valley develops the corpus 
striatum and the island of Reil. The latter is concealed 
before birth by a backward and downward growth of the 
anterior wall, forming the orbital, frontal and fron to-parietal 
opercula. The forward and downward growth of the poste- 
rior wall completes the fissure and forms the temporal lobe. 

(2) The Anterior Great Transverse Fissure, or Choroid 
Fissure. — It is produced by a curved invagination of the 
medial wall of the hemisphere vesicle. Beginning just 
behind the stalk of the vesicle, which contains the foramen 
of Monro, it extends backward to a point opposite to the 
posterior end of the optic thalamus, and then bends downward 
and forward toward the apex of the temporal lobe. It in- 
volves the entire thickness of the vesicle wall, though it is a 
permanent fissure, and the fold which it pushes into the 
lateral ventricle persists as a single layer of epithelium 
investing the choroid plexus, hence the name fissura choroid ea. 
In the developed brain the anterior great transverse (cho- 
roid) fissure is situated between the fornix and the taenia 
semicircularis. 

Thickenings. — The walls of the hemisphere vesicle thicken 
rapidly as the vesicle grows in size, and form the cortical and 
medullary substance. By the end of the second month the 
corpus striatum is well formed, near the middle of the floor 
of the hemisphere; and a ridge appears about the same time 
in the medial wall of the vesicle along the convexity of the 
anterior great transverse fissure. That ridge develops into 
a bundle of fibers constituting a lateral half of the fornix. 
Along the concave side of the same fissure another and 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 211 

slighter ridge appears which is the primitive tamia semi- 
circularis. 

Fusions. — The hemisphere vesicle so increases in size by 
the eighth week of embryonic life as to come in contact with 
its fellow of the opposite side, and with the dorsal and lateral 
surfaces of the thalamencephalon. At those two points of 
contact certain fusions occur: 

(1) Fusion of the Hemispheres with Each Other. — The 
hemisphere vesicles touch one another in front of the lamina 
terminalis. The area of contact is at first small and is 
crescentic in shape. The convexity of the crescent looks 
forward and its horns diverge backward. Along the borders 
of this crescent the two hemispheres grow together. The 
crescents themselves, remaining free, form the septum 
lucidum and inclose between them the fifth ventricle. First, 
a strong round bundle of fibers is thrown across at the 
anterior inferior angle of the crescent, which is the anterior 
commissure. Pressure of the anterior commissure against 
the lamina terminalis causes the latter to be absorbed back 
to its lining epithelium. That epithelium separates the 
commissure from the third ventricle in the adult. Second, 
fusion occurs along the concave border (the postero-inferior) 
of the crescent. That border coincides with the fornix ridge 
above referred to; and fusion of the two ridges forms the 
body of the fornix. The anterior pillar hooks around the 
foramen of Monro, and turns back into the lateral wall of the 
thalamencephalon; the posterior pillar grows backward with 
the hemisphere. Certain fibers are thrown across between 
the posterior pillars to form the commissnra hippocampi. 
Last, fusion occurs along the convexity of flic crescent, It 
forms the corpus callosum. The rostrum and genu arc first 
developed. Like the fornix, it grows with the hemispheres 



212 THE BRAIN AND SPINAL CORD. 

backward until completed. With the development of the 
corpus callosum the borders of the crescentic area are com- 
pletely fused and the fifth ventricle inclosed. 

(2) Fusion of the Hemispheres with the Thalamencepha- 
lon. — Fusion occurs between the hemisphere vesicle and the 
lateral surface and a small part of the superior surface of the 
thalamencephalon. The blending of the medial wall of the 
hemisphere and the external surface of the thalamencephalon 
is produced by the growth of that fan-shaped group of fibers 
called the superior lamina of the internal capsule. The 
growth of the fibers which form the internal capsule from the 
cortex downward and from the optic thalamus and other 
ganglia upward is the cause of that blending. On the 
superior surface of the thalamencephalon, fusion takes place 
as far medial ward as the oblique (choroid) groove on the 
optic thalamus (which see). Here the hemisphere wall is 
represented by a single layer of epithelium, which invests the 
optic thalamus on the superior surface external to the choroid 
groove. It is continuous toward the median line with the 
fold inclosing the choroid plexus; and it extends between 
the tasnia semicircular is and margin of the fornix. The 
epithelium is in continuity with the ependymal lining of the 
lateral ventricle. 

Velum Inter positum. — The growth of the meninges and 
brain vesicles occurs pari passu. The pia mater is at all 
times in contact with the surface of the vesicles; and it 
gives off branching trabecular which form the connective 
tissue network of the nerve substance. Wherever fusion be- 
tween the brain vesicles occurs, the two layers of pia are 
absorbed; and they unite with one another just beyond the 
line of fusion. Thus the pia of the hemispheres unites above 
the corpus callosum and beneath the fornix, when those 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 213 

connecting links are formed between the hemispheres. The 
pia beneath the fornix is, therefore, continuous with that 
covering the lower half of the medial wall of each hemisphere ; 
and, by growth of the hemispheres and fornix, it is carried 
back over the pia investing the thalamencephalon. Fusion of 
the thalamencephalon with each hemisphere causes absorption 
of the double layer of pia mater upward to the choroid 
groove on the thalamus and union of the two laminae along 
that groove. The result is a triangular sheet made up of 
two layers of pia, the velum interpositum. The velum inter- 
positum separates the fornix from the inter-brain in the 
mature organ. The medial part of the inferior layer of the 
velum adheres to the roof epithelium of the third ventricle 
and forms the anterior choroid tela, two longitudinal folds of 
which constitute the choroid plexuses of the third ventricle. 
The borders of the velum form the choroid plexus of each 
lateral ventricle. 

THALAMENCEPHALON. 

. This is the posterior division of the anterior primary 
vesicle. It forms the inter-brain and the third ventricle, 
except its anterior boundary. Before the anterior primary 
vesicle is divided and the thalamencephalon constricted oif 
from the prosencephalon, the optic vesicle makes its appear- 
ance on either side. It is a prominent diverticulum at hist ; 
but it grows, in man, less rapidly than the vesicle from 
which it rises. The optic vesicle becomes cupped, and is 
then the primitive retina. From it the optic nerves grow 
back to the ventral surface of the thalamencephalon, where 
they help to form the optic chiasma and tracts. Later, the 
tracts grow back along the side of the thalamencephalon, ami 
become connected with the external geniculate body, optic 
thalamus and corpora quadri gemma. 



214 THE BRAIN AND SPINAL CORD. 

The optic thalamus is formed by thickening of the lateral 
wall of the second vesicle. It fuses externally with the 
hemisphere (corpus striatum) and forms the superior lamina 
of the internal capsule. Internally, it fuses at one point 
with its fellow of the opposite side, forming the middle 
commissure. The medial surface presents a longitudinal 
groove, the sulcus of Monro, which is supposed to separate 
the ventral and dorsal zones of the thalamencephalon. A 
slight thickening of the postero-inferior wall of the thalam- 
encephalon is the primitive external geniculate body. 

From the floor of the thalamencephalon are developed the 
corpora albicantia (at first single) ; the tuber cinereum and 
infundibulum and the lamina cinerea. 

The superior wall, or roof, of this second vesicle stretches 
out and becomes very thin, except at its posterior extremity, 
where it develops a transverse white band, the posterior 
commissure. Immediately in front of this commissure, a 
diverticulum of the roof appears which is the primitive pineal 
body. Two longitudinal folds of the roof dip down into the 
ventricular cavity. These are followed by two like down- 
ward projecting folds from the inferior lamina of the velum 
interpositum, which constitute the choroid plexuses of the 
third ventricle. 

MESENCEPHALON. 

This is the embryonic mid-brain. It is the third of the 
secondary vesicles. The elbow of the mesencephalic flexure 
of 180 degrees is formed by it; and that flexure almost 
brings the thalamencephalon and epencephalon in contact 
with one another beneath it. The mesencephalon remains 
small, but its walls thicken greatly. As a result of the 
thickening, its cavity is reduced to a slender canal, the 
aqueduct of Sylvius, in the floor of which develop the nuclei 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 21 5 

of the third and fourth pairs of cranial nerves. The latter 
is developed in the constriction (isthmus of His) between the 
third and fourth brain vesicles. The walls of the mesen- 
cephalon form, ventrally, the substantia nigra and part of the 
tegmentum; and dorsally, the remainder of the tegmentum. 
The down-growth of the motor fibers of the internal capsule, 
along the ventral surface of the mesencephalon, produces the 
two crustce. About the third month the dorsal thickening is 
divided by a fore and aft groove, the sulcus longitudinalis. 
A transverse groove appears two months later and completes 
the crucial groove and the outline of the corpora quadri- 
qemina. The antero-lateral part of the roof forms the 
internal geniculate body. By the growth of fibers which 
connect the geniculate bodies with the corpora quadrigemina, 
the anterior and posterior brachia are formed. 

EPENCEPHALON". 

The* fourth brain vesicle is the rudimentary hind-brain. It 
forms the pons and cerebellum, the former from .its floor and 
the latter from its roof. Anteriorly, its cavitv contracts to 
the size of the Sylvian aqueduct; it expands posteriorly and 
is broadest at the junction of the pons with the medulla 
oblongata. The ventricular surface presents on each laternl 
wall a longitudinal furrow which divides the epoueophalon 
into a ventral and a dorsal zone. The ventral zone is com- 
posed of the floor and von fro-lateral, or basal, laminae, and 
the dorsal zone is made up of the roof and dorso-ln feral, or 
alar, lamina 5 . We shall find this division continued in the 
motoncephalon and the spinal part of the neural tube. 

Cerebellum. — A long transverse thickening may be ob- 
served in the anterior part of the eponoophalon-roof ;is earl? 
as the second month. The posterior part of the roof remains 
thin. At the third month that ridge presents a median 



2l6 THE BRAIN AND SPINAL CORD. 

enlargement, divided by three transverse fissures, which is 
the embryonic valve of Vieussens and vermis cerebelli. The 
lateral portions of the transverse ridge grow rapidly after the 
third month. They form the cerebellar hemispheres. At 
first the hemispheres are smooth, but they become lobulated 
about the fifth month and foliated a month later. The cere- 
bellar peduncles are completed at the same time. The infe- 
rior appear first and produce a prominent ridge in each 
lateral wall of the epencephalon at the third month. A 
month later the middle peduncles are formed and the superior 
are completed about the fifth month. The peduncles are 
produced by the growth of axones from various masses of 
neuroblasts. 

Pons. — The pons develops simultaneously with the cere- 
bellum. The ventral zone of the epencephalon thickens 
greatly. The neuroblasts formed therein constitute the 
nuclei of the pons and of the reticular formation, and the 
motor nuclei for the fifth, sixth and seventh pairs of cranial 
nerves; the dorsal lamina, in the lateral wall of the epence- 
phalon, produces the neuroblasts which form the superior 
olivary nucleus and the superior terminal nucleus of the 
sensory part of the trifacial nerve. From the nucleus pontis 
axones ascend through the lateral walls of the epencephalon 
to the cerebellum and others descend from the cerebellum 
by the same course to the pons. They form the middle cere- 
bellar peduncles. At the same time, about the fourth month, 
the motor tracts composing the crustse of the mid-brain grow 
downward into the ventral portion of the pons and the 
fronto-pontal and temporo-pontal tracts and part of the 
pyramidal tracts end in the nuclei pontis. The pyramidal 
fibers to motor nuclei of bulbar and spinal nerves grow down 
through the pons intersecting its transverse fibers. 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 21? 
METENCEPHALON. 

. The metencephalon is constricted off from the epence- 
phalon at the twenty-eighth day; but, later, that constric- 
tion largely disappears and the common cavity of the two 
vesicles, broad in the middle and contracted to a slender 
canal at each end, persists as the fourth ventricle of the 
mature brain. Like the epenoephalon, the fifth brain vesicle 
is divided at the third week into a ventral and a dorsal zone 
by a deep furrow on the ventricular surface of each later 
wall. That lateral furrow, as regards position, is represented 
in the mature organ by the dorso-lateral groove on the ex- 
terior surface of the medulla and it actually persists in the 
superior and inferior fovea of the fourth ventricle. The 
anterior and lateral columns of the medulla, which are an- 
terior to the dorso-lateral groove, are therefore developed in 
the ventral zone; and the structures situated behind the 
dorso-lateral groove, namely, the posterior columns, the resti- 
form bodies and the roof epithelium are formed in the dor- 
sal zone. 

The roof of the anterior half of the metencephalon 
stretches out widely and remains a single layer of epithelial 
cells. It forms no nerve tissue. Other portions of the 
metencephalon develop quite uniformly. But by the expan- 
sion of the roof, just mentioned, the anterior extremities of 
the lateral walls are pushed outward and forward almost to 
the plane of the floor, and a transverse section of the vesicle 
in that region presents the form of a very broad capital V 
with the roof epithelium stretching between the two arms 
and converting the letter into a triangle. Transverse sec- 
tion through the lower half of the metencephalon at the 
third or fourth week shows an elongated ellipse with a dorso- 
ventral major axis. 



218 THE BRAIN AND SPINAL CORD. 

Internal Surface. — The lateral wall, in both upper and 
lower regions, presents the longitudinal groove which sepa- 
rates the ventral and dorsal zones. The median ventral 
groove persists throughout and the lateral grooves are repre- 
sented by the fovea of the fourth ventricle. The low 
eminence situated between the median and each lateral 
groove becomes the fasciculus teres. 

External Surface. — On the external surface of the 
metencephalon and along the ventral border of the dorsal 
zone, there appears very early an oval bundle of descending 
fibers, called the solitary bundle. It is composed of axones 
from the jugular and petrosal ganglia, and constitutes the 
descending root-fibers of the ninth and tenth pairs of nerves. 
At about the same time axones from the Gasserian ganglion 
form a bundle of descending fibers on the lateral surface 
dorsal to the solitary bundle. They constitute the so-called 
ascending root of the tri-facial nerve. Soon after the ap- 
pearance of the solitary bundle and the "ascending" root 
of the fifth nerve, the posterior margin of the dorso-lateral 
lamina is folded outward and forward until it rests upon 
the external surface. That fold covers both the above bun- 
dles of fibers and places them in the position \hvy occupy in 
the mature brain. 

The substance of the metencephalon, like other divisions of 
the neural tube, presents, under the microscope, three dis- 
tinct zones at the fourth week of embryonic life. The outer 
layer is composed of neuroglia ; the middle, or mantle, layer 
of neuroblasts; and the inner, or ependymal, layer is made 
up of columnar epithelial cells. 

The cells of the inner layer become ciliated and form the 
lining of the ventricle. 

The mantle, or middle, layer undergoes most develop- 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 2IO. 

ment. Its neuroblasts form the formatio reticularis and the 
cranial nerve and other nuclei of the medulla oblongata. In 
the dorsal zone the neuroblasts form the terminal nuclei for 
the eighth, ninth and tenth cranial nerves and the nucleus 
gracilis, nucleus cuneatus and nucleus of Eolando. As early 
as the fourth week axones may be traced from the last three 
nuclei, ventro-medially, toward the point where they very 
soon form the sensory, or fillet, decussation. Neuroblasts 
which have wandered from the dorsal zone form the olivary 
and accessory olivary nuclei quite late in intra-uterine life 
(6th month). From the neuroblasts of the ventral zone are 
developed the gray matter and fibers of the formatio reticu- 
laris alba et grisea, and the motor nuclei of the twelfth, 
eleventh (accessory part), tenth and ninth pairs of cranial 
nerves. 

The neuroglia layer forms the supporting matrix for the 
tracts of fibers, and the raphe of the medulla. By the third 
month the fasciculus gracilis, fasciculus cuneatus and fasci- 
culus of Eolando, extensions of GolFs and Burdach's columns 
in the cord, have grown up to their terminal nuclei in the 
medulla. The restiform body is at that time well developed, 
and the tracts of the lateral area of the medulla are visible. 
The posterior longitudinal bundles appear near the median 
raphe in the ventral zone at about the same time ; and, ven- 
tral to them, fibers from the sensory decussation form the 
interolivary fillets. The great motor tracts from the Ro- 
landic area of the cortex reach the medulla at the fourth 
month. Growing downward, on either side of the median 
line, they conceal the interolivary fillets and form the pyra- 
mids of the medulla oblongata. The form of the medulla 
is completed two months later (the 6th month) by the ap- 
pearance of the olivary bodies. 



220 THE BRAIN AND SPINAL CORD. 

SPINAL CORD. 

That portion of the neural tube which is situated behind 
the metencephalon is the embryonic spinal cord. It is of 
nearly uniform size from cephalic to caudal end. Pos- 
teriorly, it is open into the alimentary canal for a short time. 
The lumen of the neural tube is at first large and elliptical 
in shape. Later, at the sixth week, it has a diamond shape, 
the acute angles of the diamond being formed by the roof 
and floor of the canal, and it is lined with columnar ciliated- 
cells. As the walls thicken the canal is contracted more and 
more until it reaches the capillary size of the adult cord. It 
is continuous with the fourth ventricle above and dilates to 
form the inferior rhomboid fossa in the filum terminale. 
The neural tube forms the whole substance of the spinal cord, 
with the exception of the great motor tracts that grow into it 
from the brain, and the sensory tracts and fibers that enter it 
from the spinal and s}^mpathetic ganglia. At the sixth week 
of embryonic life the anterior and posterior roots of the 
spinal nerves are clearly seen; they are horizontal in direc- 
tion. The cord extends the entire length of the spinal canal 
until the third month, when the caudal end begins to recede. 
It reaches only to the third lumbar vertebra at birth and, 
in the adult, but to the lower border of the first lumbar 
vertebra. With the rapid growth of the spinal column, the 
roots of the lumbar, sacral and coccygeal nerves become 
greatly elongated and, together with the filum terminale, 
form the cauda equina. Meninges. — The investing meso- 
blast of the neural tube develops the meninges of the spinal 
cord. 

Zones. — By the sixth week of intra-uterine life the neural 
tube is divided into a ventral and a dorsal zone -by a lateral 
groove on either side continuous with those dividing the 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 221 

metencephalon and epencephalon. The tube presents ex- 
ternally, opposite to each lateral groove, a furrow called the 
central fissure, which is occupied later by the crossed pyra- 
midal tract. The whole of the spinal cord anterior (or ven- 
tral) to the cervices of the posterior cornua of gray matter 
is represented by the ventral zone. In the dorsal zone, the 
heads of the posterior cornua and the posterior columns are 
developed. The cervix of each posterior horn is formed by 
the thin lamina connecting the two zones. 

Three Histologic Layers. — At a time somewhat earlier 
than the division into ventral and dorsal zones, even at the 
fourth or fifth week, the spinal part of the neural tube pre- 
sents three microscopic layers, like those seen earlier in the 
metencephalon and other brain vesicles. 

The outer layer, composed of neuroglia, is very thin except 
in the floor of the tube on either side of the median line; 
and later, in the corresponding parts of the roof. In those 
situations are formed the anterior and posterior columns of 
the cord. The central fissure (see above), also, presents a 
thickening of neuroglia through which grow the crossed 
pyramidal and direct cerebellar tracts. 

The second layer is gray matter. It is the mantle layer 
and contains the neuroblasts. At the fourth or sixth week 
it is very thick, comprising nearly all of the neural tube. 
The H-shaped column of gray substance is derived from this 
layer. In the ventral zone the neuroblasts collect near the 
floor of the tube and form a large column on either side of 
the median line. The axones of the more ventrally located 
neuroblasts (anterior cornua) grow contrifugally out of the 
antero-lateral surface of the neural tube. They form the 
anterior roots of the spinal nerves. The more dorsally lo- 
cated neuroblasts develop axones also; but ou account of 



222 THE BRAIN AND SPINAL CORD. 

meeting resistance, according to His, they become longi- 
tudinal and form the ground bundles of the cord and the 
antero-lateral ascending cerebellar and direct cerebellar 
tracts. The gray matter in the dorsal zone becomes trans- 
formed into the heads of the posterior cornua; its neuro- 
blasts form only intrinsic neurones, their processes remaining 
in the gray substance. Axones from the spinal ganglia, 
forming the posterior roots of the spinal nerves, grow into 
the dorsal zone; and each axone divides T-like into a small 
descending and a large ascending branch, and also gives off 
many collaterals both before and after division. The ascend- 
ing fibers for a time form the oval bundle of His on the 
surface of the tube; later, they constitute the tract of Lis- 
sauer, most of Burdaclr's and all of Golfs columns. 

The third layer, the ependymal layer, lines the ventricle. 
It is composed of neuroglia covered, internally, by columnar 
ciliated cells, which appear about the fifth week. 

The Longitudinal Tracts. — The white columns of the 
spinal cord are formed in the superficial, or neurogliar, layer. 
At first they are composed of non-medullated fibers, and it is 
a remarkable fact that the various tracts receive their 
myeline sheaths at definite periods between the fifth and 
ninth months of intra-uterine life (Flechsig). The ground 
bundles and the posterior columns first appear. They may be 
seen at the sixth week. The ascending cerebellar tracts fol- 
low. And the descending cerebellar and the direct and 
crossed pyramidal tracts are last to appear; they are not 
developed before the fourth or fifth month. According to 
Flechsig the tracts of the spinal cord are medullated as 
follows : 

1. The ground bundles of the posterior columns at about 
the fifth month. 



EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 223 

2. The ground bundles of the anterior columns about the 
sixth month. 

3. The ground bundles of the lateral columns from the 
fifth to the seventh month (antero-lateral mixed, one, 5-7 
month, and lateral limiting layer, 6 months). 

4. The column of Goll and Burdach (excepting ground 
bundles) between the sixth and seventh months. 

5. The direct cerebellar tract at the seventh month. 

6. The antero-lateral cerebellar tracts, ascending and de- 
scending, at the eighth month.- 

7. The direct and crossed pyramidal tracts at the ninth 
month. 

Fissures.— The so-called Posterior Median Fissure is in 
reality a septum of neuroglia. At no time is it a true fis- 
sure. It appears to be formed by the approximation of the 
lateral walls of the neural canal. After the sixth week the 
approximation begins at the roof and gradually proceeds 
ventrally to the center of the cord. The ependyma which 
originally lined the dorsal part of the canal is thus fused 
into the posterior median septum of neuroglia. 

The Poster o-lateral Fissure is the groove between the lat- 
eral border of the posterior column and the dorsal border of 
the lateral column. It is the development of the posterior 
and lateral columns that produces this fissure. The em- 
bryonic central fissure is obliterated and the postero-lateral 
surface of the cord rendered prominent by the formation of 
the direct cerebellar and crossed pyramidal tracts. 

Anterior Median Fissure. — That is a true fissure. Tt be- 
gins to be formed at the sixth week, when the earliest fibers 
of the antero-lateral ground bundle are developed. Tt deepens 
with the growth of the antero-lateral <rrormd bundle and is 
completed, in the fourth or fifth month, by the descent of 



224 THE BRAIN AND SPINAL CORD. 

the direct pyramidal tract. Those two tracts cause a bulging 
in the ventral surface on either side of the median line 
which increases with the medullation of the pyramidal tracts 
in the ninth month; and the ridges thus produced, failing 
to fuse completely, become the walls of th anterior median 
fissure. The partial fusion which does occur between the 
two ridges is due to the formation of the anterior commis- 
sure of the cord. 



INDEX 



A 

PAGE. 

Abducens nerve 129, 140, 155 

Accessory nucleus cuneatus 143, 147 

Accessory nucleus of ninth and tenth cranial nerves. 152 

Accessory sensory roots of ninth and tenth cranial nerves 145 

Acervulus cerebri. 46 

Acustic area 153 

Acustico-cerebellar tract 114 

Acustic radiations 26, 51, 63, 81, 90, 122 

Acustic striae 151 

Acustic trigone . . 151, 153 

Acustic tubercle 153 

Afferent, or sensory, conduction paths 190-197 

After-brain, or medulla oblongata 7, 128-149 

Alae cerebelli 105 

Ala cinerea 152 

Alar lamina (or dorso-lateral) 215 

Alveus of hippocampus 41, 75 

Amygdala 25, 26, 37, 40 

Anastamotic vein of Trolard 99 

Angular convolution 12 

Annectant convolutions 14 

Anosmia 75 

Ansa lenticularis 56, 77, SO, S4, 89 

Ansa peduncularis 26, 56, 79, 89 

Anterior association center 71 

Anterior brachium 51, 59, 82, 215 

Anterior cerebellar notch 101 

Anterior cerebral arteries 95, 96 

Anterior choroid tela 5, 44, 46, 213 

Anterior communicating arteries 95 



INDEX. 

PAGE. 

Anterior choroid artery 117 

Anterior commissure of cerebrum 7, 31, 43, 47, 211 

Anterior commissure of cord 165, 171, 172, 224 

Anterior cornu 166, 168 

Anterior cornu of lateral ventricle 38 

Anterior crescentic lobules of cerebellum 106 

Anterior external arciform fibers 130, 131 

Anterior great transverse fissure (or choroid) 213 

Anterior horn of gray matter 146 

Anterior inferior cerebellar artery 117 

Anterior longitudinal bundle 62, 82, 88, 124, 140, 173, 174 

Anterior median fissure of cord 163, 164, 223 

Anterior median fissure of medulla 128 

Anterior nucleus of optic thalamus 78 

Anterior olfactory lobule 22 

Anterior orbital convolutions 22 

Anterior perforated lamina 22 

Anterior pillars' of fornix 43, 44, 48, 79 

Anterior quadrigeminal body 76, 82 

Anterior root of spinal nerves 180 

Anterior segment of internal capsule 27 

Anterior spinal artery . . . ' 161, 182, 183 

Anterior stalk of thalamus 28, 49, 80, 90 

Anterior tubercle of optic thalamus 50 

Anterior white column of cord 167 

Antero-lateral ascending cerebellar tract . . .115, 131,140-142, 170, 174 

Antero-lateral descending cerebellar tract 

116, 131, 132, 140,141,144,168, 174 

Antero-lateral fissure of cord 164, 165 

Antero-lateral ganglionic arteries 96 

Antero-lateral ground bundle 131, 140, 141, 173, 174 

Antero-median ganglionic arteries. 96 

Apertura mediana ventriculi quarti 5, 133 

Aperturae laterales ventriculi quarti 5, 133 

Apex columnae posterioris 169 

Apex cornu posterioris 169 

Apparent central termination of posterior spinal roots 181 

Aqueduct of Sylvius 42, 43, 44, 58, 150, 214 

II 



INDEX. 

PAGE. 

Arachnoid of brain 4 

Arachnoid of spinal cord 160 

Arachnoidea encephali 4 

Arachnoidea spinalis 160 

Arbor vitae 114 

Arciform fibers 1 16, 132, 135, 144, 147, 178 

Arcif orm nucleus 149 

Arcuate association fibers of cerebrum 91 

Area acustica 153 

Area of Broca 22 

Area of cerebral softening 97 

Area of general sensation 13 

Area parolfactoria (Broca) 24 

Areas of medulla 136, 137 

Arteria basilaris 96 

Arteria cerebri anterior 95 

Arteria cerebri media . , 95 

Arteria cerebri posterior 96 

Arteria choroidea anterior 38, 97 

Arteria choroidea postero-lateralis 97 

Arteria choroidea postero-medialis 98 

Arteria communicans anterior 95 

Arteria communicans posterior 95 

Arteria meningea media 3 

Arteria spinalis anterior 161, 182 

Arteria spinalis posterior 161, 182 

Arteriae choroideae 97 

Arteries of dura mater 3 

Arteries of pia mater 6 

Artery of cerebral hemorrhage 97 

Ascending frontal convolution 11 

Ascending parietal convolution 11, 12 

Ascending tracts of spinal cord 172 

Association fibers of cerebrum 85, 91 94 

Association fibers of cerebellum 117 

Auditory center (sensory) 71 

Auditory conduction paths 63, 83. 90, 122, 195 Wl 

Auditory cortex 86, 98 

hi 



INDEX. 

PAGE. 

Auditory lobes 83 

Auditory memories 71, 93 

Auditory nerves , 137, 144 

Auditory radiations (see acustic radiations). 

Auditory reflex 200 

Aula of third ventricle 34, 42 

Axones (or neuraxanes) 66, 67 

B 

Basal lamina (ventro-lateral) 215 

Basal or inferior surface of cerebrum 17, 24 

Basis (es) pedunculi cerebri 7, 20, 25, 33, 53, 54 

Basket cells of cerebellum 112 

Biventral lobule 1 10 

Blood supply of cerebrum and midbrain .94-99 

Blood supply of cerebellum 117 

Blood supply of pons 127 

Blood supply of medulla oblongata 158 

Blood supply of spinal cord 182-184 

Body of lateral ventricle 35 

Borders of corpus callosum 29 

Boundaries of fourth ventricle 150 

Brachia pontis 103, 115, 119, 121 

Brachium conjunctivum 64, 102, 115, 120, 127, 150 

Brachium posterioris 122 

Brachium quadrigeminum inferioris .....' 60 

Brachium quadrigeminum superioris 59 

Brain sand 146 

Brain vesicles and derivatives 207, 208 

Bulb of caudate nucleus 37 

Bulbus olfactorius 22, 122 

Burdach's column 177, 178 

C 

Calamus scriptorius , 103, 145 

Calcar avis 39 

Calcarine fissure 15 

Calloso-marginal fissure 14 

IV 



INDEX. 

PAGE. 

Canalis centralis spinalis 163 

Capsula externa 25 

Capsula interna 25, 26, 28, 31, 35, 36, 53, 54, 55, 211 

Caput columnse posterioris 169 

Caput cornu posterioris 169 

Caput nuclei caudati 37 

Cardio-accelerator center 168 

Cauda equina 161 

Cauda nuclei caudati 37 

Caudate nucleus 25, 31, 35, 39, 40, 76 

Cavernous sinus 3 

Cavum septi pellucidi 34 

Cavum subarachnoidiale 5 

Cavum anterius and posterius 160 

Cells of anterior cornu of spinal cord 167 

Cells of Max Schultze 23 

Cells of posterior cornu 169, 170 

Cells of Purkinje Ill 

Center of gray crescent of spinal cord 167 

Center of hearing 14, 71 

Center of taste, smell, hearing 13, 71 

Center of vision 8, 71 

Central canal of spinal cord 150, 163 

Central fissure (of cerebrum) 10 

Central fissure (embryonic cord) 221 

Central ligament of spinal cord 161 

Central lobe 14 

Central lobule and alas of cerebellum 105 

Central nucleus of thalamus 79 

Central, or ventricular, gray matter of cerebrum 70, 84, 85 

Centrifugal arteries of cord 183 

Centrifugal fibers of corpus striatum 77 

Centrifugal projection fibers of cerebrum So 89 

Centripetal arteries of cord [83 

Centripetal fibers of corpus striatum 77 

Centripetal projection fibers of cerebrum 89-81 

Cerebellar hemispheres \00 

Cerebellar notches 101 



INDEX. 

PAGE. 

Cerebello-olivary tract . . 116, 132, 136, 144, 148 

Cerebral hemispheres 7, 8 

Cerebellum 7, 100-118 

Cerebro-corticopontal paths 186, 187 

Cerebro-corticopontal tracts, frontal 56, 85 

Cerebro-corticopontal tracts, temporal 55, 85 

Cerebrum 7-99 

Cervical enlargement of spinal cord 163 

Cervix volumnae posterioris 169 

Cervix cornu posterioris 169 

Chapter I 1-8 

Chapter II 9-51 

Chapter III 51-65 

Chapter IV 66-99 

Chapter V 100-127 

Chapter VI 127-149 

Chapter VII 150-158 

Chapter VIII 159-161 

Chapter IX 162-184 

Chapter X 185-200 

Chapter XI 201-224 

Charcot's artery 97 

Choroid arteries 97, 98 

Choroid fissure 2, 9, 10, 15, 41, 213 

Choroid groove of thalamus 49, 212 

Choroid plexus of fourth ventricle . 1 33, 151 

Choroid plexus of lateral ventricle 35, 38, 40, 46, 213 

Choroid plexus of third ventricle ■. 43, 45, 48, 213, 214 

Choroid vein 38, 98 

Cilio-spinal center 168 

Cingulum 92 

Circle of Willis 94 

Circular sinus 3 

Circulus arteriosus 94 

Cisterna cerebello-medullaris 5 

Cisterna chiasmatis 5 

Cisterna interpeduncularis 5 

Cisterna pontis 5 

VI 



INDEX. 

PAGE. 

Clark's column of cells 168 

Claustrum 25, 76 

Clava 133, 143, 147 

Clivus and posterior crescentic lobules 106 

Cochlear nucleus (i) 63, 144, 153 

Collateral fissure 16 

Colliculi of corpora quadrigemina 54, 59, 82, 83 

Colliculus facialis 102 

Columna (ae) anterior in medulla 146 

Columna (ae ) in spinal cord 165, 166 

Columna (ae) fornicis 32 

Columna (ae) lateralis 166 

Columna (as) posterior in medulla 147 

Columna (ae) in spinal cord 165, 166, 169 

Column of Clark 168, 169 

Column of Burdach 177, 178 

Column of Goll 179 

Column of Gowers 175 

Column of Loewenthal 175 

Column of Turck 174 

Column of Waldeyer 168 

Comma tract 170, 178 

Commissura anterior alba 165, 167, 171, 172 

Commissura anterior cerebri 47 

Commissura hippocampi 7, 32, 91, 211 

Commissural fibers of cerebellum 116 

Commissural fibers of cerebrum 85, 91 

Commissure of Gudden 20, f> I 

Commissure of Meynert 81 

Conduction paths 185-201 

through anterolateral ascending cerebellar tract 192, 193 

antero-lateral ground bundle and formatio reticularis. . 193 

cerebro-corticopontal tracts 186, 1 S T 

cochlear nerve 195 

columns of Goll and Burdach 190, 191 

cranial nerves and medial fillet 191 

direct cerebellar tract 191, 192 

Eormatio reticularis 189, W 

VII 



INDEX. 

PAGE. 

intermediate bundle of crusta 187, 188 

ninth nerve and corda tympani 197 

olfactory nerves, tract, &c 194 

optic nerves, tract, &c 194, 195 

pyramidal tracts 185, 186 

red nucleus 188 

vestibular nerve 196, 197 

Confluens sinuum 2 

Conjugate deviation , 127, 189 

Connective tissue of brain and cord 76 

Conus medullaris 163 

Conus terminalis 163 

Convolutions or gyri 9 

Cornu ammonis (hippocampus major) 73 

Cornu commissural tract 170, 178 

Cornua of lateral ventricle 38-42 

anterior 38, 39 

middle 39-42 

posterior 39 

Cornu (a) ventriculi lateralis 39-42 

anterius 38, 39 

inferius • 39-42 

posterius 39 

Corono radiata 28 

Corpus (ora) albicans £ajitia) 7, 18, 19, 33, 44, 57, 214 

callosum 7, 8, 28, 30, 35, 39, 91, 211, 212 

dentatum (a) 113 

fimbriatum (a) 40 

fornicis '. 32, 92 

geniculatum laterale 51, 82 

geniculatum mediale 51, 60, 82 

mamillare (ia) 19 

medullare (cerebelli) 101, 114 

pineale 45 

quadrigeminum (a) 7, 31, 51, 54, 57, 59, 60, 166 

restiforme (ia) 102, 11H, 132, 144, 150 

striatum (a) 7, 25, 35, 55, 56, 76, 84, 210 

Cortex near calcarine fissure 74 

VIII 



INDEX. 

PAGE. 

Cortex near Sylvian fissure 75 

Cortical fillet 80, 90 

Cortical gray matter of cerebellum 111-113 

Cortical gray matter of cerebrum 70-76 

Cranial reflexes 199 

Cranial and spinal reflexes 200, 201 

Crossed descending tract from red nucleus 65, 88, 125, 142, 176 

Crossed paralysis 127, 149 

Crossed pyramidal tract 130, 143, 147 

Crossing of main sensory path 170 

Crura ad cerebrum 102 

Crura ad medullam 102 

Crura ad pontem 103 

Crus cerebri 7 

Crus fornicis 32 

Crusta (ae) ..7, 53-56, 66, 85-89, 215 

Culmen monticuli cerebelli 106 

Culmen and anterior crescentic lobules 106 

Cuneate lobe 17, 90 

Cuneate nucleus 132 

Cuneate tubercle .. . . . 133, 147 

Cuneus 17 

D 

Declive monticuli cerebelli 106 

Decussatio lemniscorum 136 

Decussation of pyramids 129, 130 

Deep nuclear, or rust-colored granular layer of cerebellum. .112, 113 

Deep origin of anterior root of spinal nerves ISO 

Deep origin of posterior root of spinal nerves 181, 182 

Defecation center 16S 

Defecation reflex 198, 199 

Degeneration of Nissl 68 

Degeneration of Waller 68 

Dendrites 66 

Dentate fascia. . 40, 1 1 

Derivatives of brain vesicles 807, 208 

Descending tracts of cord 172. ITS 



INDEX. 

PAGE. 

Descending root of trifacial nerve 88, 125 

Development of brain 205-219 

Development of cerebrum 208-214 

Development of olfactory lobe 208 

Development of interbrain 213, 214 

Development of midbrain .214, 215 

Development of cerebellum 215, 216 

Development of pons varolii 216 

Development of medulla oblongata 217-219 

Development of spinal cord 220-224 

Diaphragm sellae . 2 

Diencephalon 7, 42, 205 

Digitationes hippocampi 41 

Digastric lobules of cerebellum '. 110 

Direct cerebellar tract 116, 132, 142, 144, 169, 175 

Direct pyramidal tract 130, 138, 174 

Dorsal surface of pons 120 

Dorsal transverse fibers of pons 121 

Dorsal deep transverse fibers of pons 121 

Dorsal deep longitudinal fibers of pons 123 

Dorsal longitudinal fibers of pons , 125 

Dorsal nucleus of auditory nerve 153 

Dorsal surface of medulla 13.2 

Dorsal zone of embryo 205, 214, 215, 217, 219, 220 

Dorso-lateral groove of medulla 129 

Dorso-ventral fibers of medulla 136, 137 

Dorso-lateral cerebellar tract 175 

Dorso-ventral fibers of spinal cord 172 

Dura mater encephali 1 

Dura mater of spinal cord 159, 160 

Dura mater spinalis 159, 160 

E 

Edinger's bundle 77, 84 

Efferent or motor paths 185-190 

Eighth cranial nerve r. . . 144 

Ejaculation center 168 

Eleventh nerve 131 

x 



INDEX. 

PAGE. 

Embryology of brain and spinal cord 202-224 

Eminentia acustici 153 

Eminentia cinerea 152 

Eminentia collateralis 40 

Eminentia medialis 152 

Eminentia teres 145, 151, 152 

End-brush 67 

End-arteries of Cohnheim 97 

End-organs 66 

Enlargements of spinal cord 163 

Epencephalon 205, 215, 216 

Ependyma 34 

Epiphysis cerebri (see pineal body) 

Epithalamus 78 

Erection center 168 

Exceptions to typical cortex 74 

Exterior surface of cerebrum 9 

External accessory olivary nucleus 148 

External arciform fibers 116, 132, 135, 144, 147 

External capsule 25 

External geniculate bodies 7, 49, 50, 60, 76, 82, 90 

External nucleus of optic thalamus (or lateral) 78 

Extremities of optic thalamus 49 

F 

Facial nerve 135 

Facial paralysis 127. 189 

Facies anterior (medulla?) 130 

.Fades basalis cerebri 17 

Facies cerebelli inferior 107 

Facies cerebelli superior L03 

Facies convexa 9 

Facies lateralis 131 

Facies medialis 14 

Facies posterior (medulla) 134 

Falx cerebelli 1 

Falx cerebri I 

Fascia dentata hippocampi 11 

\i 



INDEX. 

PAGE. 

Fasciculus antero ateralis superficialis (ascendens, descendcns) 

131, 141, 174 

Fasciculus cerebello-spinalis 144, 175 

Fasciculus cerebro-spinalis anterior (ventralis) 138, 174, 176 

Fasciculus cerebro-spinalis lateralis 138, 176 

Fasciculus cuneatus 132, 142, 143, 150, 1 77, 219 

Fasciculus gracilis 132, 142, 143, 150, 179, 219 

Fasciculus longitudinalis (inferior) .' 93 

Fasciculus longitudinalis (medialis) 61, 124, 139, 173 

Fasciculus longitudinalis (superior) 93 

Fasciculus longitudinalis pyramidalis pontis 55, 86, 122 

Fasciculus longitudinalis ventralis 140 

Fasciculus marginalis 177 

Fasciculus occipito-frontalis 93 

Fasciculus perpendicularis 94 

Fasciculus proprius antero-lateralis 131, 141, 173 

Fasciculus retroflexus 79, 84 

Fasciculus Rolandi 132, 142, 143, 219 

Fasciculus solitarius 145, 218 

Fasciculus tegmenti centralis 64, 124 

Fasciculus teres 145, 218 

Fasciculus thalamo-mamillaris 20, 33, 79 

Fasciculus triangularis (Helwigi) 64 

Fasciculus uncinatus 93 

Fasciculus ventralis 124, 174 

Fastigium (ventriculi quarti) 114, 151 

Fibers of internal capsule 85-90 

Fibers of tegmentum 60-65, 89 

Fibrae arcuatae external anterior, posterior 131, 135 

Fibrae cerebello-olivares 136, 148 

Fibrae pontis superficiales 121 

Fifth temporal, infracalcarine or lingual convolution 17 

Fifth ventricle 33, 212 

Fillet 50, 62,' 123, 124 

Fillet decussation 136, 219 

Fillet of gyrus fornicatus 92 

Filum terminale 161, 163 

First temporal convolution 14 

XII 



INDEX. 

PAGE. 

First temporal sulcus 13 

Fissura calcarina 45 

Fissura choroidea 9, 16 

Fissura collateralis 16 

Fissura hippocampi 15 

Fissura lateralis cerebri 10 

Fissura longitudinalis cerebri 9 

Fissura mediana anterior, posterior 128, 132, 163, 164 

Fissura prima 22, 24, 30 

Fissura transversa cerebri 9 

Fissurae interlobulares 10, 104 

Fissurae orbitales 22 

Fissural ventricle (see fifth ventricle). 

Fissural veins , 183 

Fissure of Rolando 10 

Fissure of Sylvius 10 

Fissures of convex surface of cerebrum 9-11 

Fissures of inferior surface of cerebrum 51 

Fissures of lower surface of cerebellum 107, 108 

Fissures of medial and tentorial surface 14-16 

Fissures of spinal cord 163-165, 223, 224 

Fissures of superior surface of cerebellum 104, 105 

Fissures or sulci 9 

Flexures of nural tube 206 

Flocculi (cerebelli) 109, 151 

Floor of fourth ventricle 151 

Folium cacuminis and posterior lobules of cerebellum 106 

Folium vermis : 107 

Foramen caecum of Vicq d'Azyr 130 

Foramen interventriculare (Monroi) 34, 43 

Foramen of Magendie 5, 133. L50 

Foramen of Monro 32, 34, 42. 43. 41. 20s. mi 

Foramen of Key and Retzins 5, 133, 150 

Forceps major 39 

Formatio reticularis alba 138, 139 

Formatio reticularis grisea 140 

Formatio reticularis of medulla 134 

Fornix,,.. 7. 31, 32. 35. 92, 210, 21 1 

XIII 



INDEX. 

PAGE. 

Fossa interpeduncularis 53 

Fossa rhomboidea inferior 163 

Fourth cranial nerve 53. 120 

Fourth temporal, or fusiform, convolution IT 

Fourth ventricle 100, 129, 150-158, 217 

Fovea inferior 152, 153, 218 

Fovea superior 151, 218 

Fraenula icerebelli) 105 

Frontal lobe 11 

Fronto parietal operculum 10, 12, 22 

Fronto-pontal tract 27, 86 

Function of cerebellum 100 

Function of nllet 62 

Functions of neurones 68 

Functions of stellate, basket and granule cells 113 

Funiculus anterior and f . lateralis 167 

Funiculus antero-lateralis 173 

Funiculus lateralis ' 131, 169 

Funicilus posterior 169, 177 

Fusiform cell bodies of cortex 74 

functions of 74 

Fusions of hemispheres with each other 211 

Fusions of hemispheres with thalamencephalon 211 



Ganglion interpedunculare 57 

Ganglion spinale 181 

Ganglionar gray matter of cerebellum 113 

Ganglionar gray matter of cerebrum and midbrain 70-85 

Ganglionic system of arteries 96, 97 

General cavity of cerebrum 30 

General sensory paths 190-193 

Genital centers 168 

Genu and truncus of corpus callosum 30, 31, 39 

Genu of facial nerve 61, 140, 146 

Genu of internal capsule 27, 86 

Germinating cells i Hisj 204 

xiv 



INDEX. 

PAGE 

Globus pallidus ? 36, 64 

Glossopharyngeal nerve 137, 156 

Goll's column 143, 179 

Gower's column. 175 

Gracile nucleus 132 

Grand divisions of brain 6, 7 

Granulationes arachnoideales 3 

Gray and white matter of cerebrum and midbrain 66-99 

Gray commissure of cord 168 

Gray crescent of cord 165-171 

Gray matter of brain and cord 68 

Gray matter of cerebellum 103 

Gray matter of cerebrum and midbrain 70-85 

Gray matter of cord 165-171 

Gray matter of formatio reticularis pontis 126 

Gray matter of medulla 146, 149 

Gray matter of pons 126, 127 

Great longitudinal fissure 8, 9 

Great transverse fissure 5, 31, 40, 49 

Gudden's commissure 20, 51 

Gustatory conduction paths 197 

Gyri insulas-Gyri breves-Gyrus longus 14 

Gyri occipitales laterales 13 

Gyri operti 14 

Gyri orbitales 22 

Gyrus angularis 12 

Gyrus centralis, anterior, posterior 11, 12 

Gyrus cinguli 16 

Gyrus fornicatus 16 

Gyrus frontalis, superior, medius, inferior 11 

Gyrus fusiformis 17 

Gyrus hippocampi ' 16 

Gyrus lingualis 17 

Gyrus rectus 22 

Gyrus supramarginalis 12 

Gyrus temporalis superior, medius, inferior II 



w 



INDEX. 
u 

PAGE. 

Habenula \ 45 

Hatteria 46 

Helwig's triangular tract 124, 141, 148, 175 

Hemispheres of cerebellum 100 

Hemispheres of cerebrum 7, 8 

Hemisphere vesicle 208 

Hemispherium cerebelli 100 

Hemispherium cerebri _ 7, 8 

Hind-brain 7, 100-127 

Hippocampal convolution 16 

Hippocampal fissure ' 15 

Hippocampus 40 

Hippocampus major 40, 75 

Hippocampus minor 39 

Histologic layers of embryo 205, 218, 219, 221, 222 

Histologic layers of spinal cord 221, 222 

H-shaped column of gray matter in medulla 146, 166 

Hylus nuclei dentati 113 

Hypophysis cerebri 19 

Hypoglossal nerve 129, 131, 137, 156 

Hypoglossal trigone 145, 152 

Hypothalamic body 50 

Hypothalamic nuclei 48 

Hypothalamic tegmental region 50, 53 

Hypothalamus 50 



Indirect motor paths 55, 56, 86 

Inferior cerebellar veins 118 

Inferior cerebral veins 98, 99 

Inferior fovea 152, 153, 218 

Inferior frontal convolution 11 

Inferior frontal sulcus 11 

Inferior gray commissure of cerebrum 19 

Inferior lamina of internal capsule 26, 40 

Inferior lamina of medullary stem 101, 114 

Inferior longitudinal fasciculus 93 

XVI 



INDEX. 

PAGE. 

Inferior longitudinal sinus ...2, 47 

Inferior medullary vellum 101, 133, 150 

Inferior occipital convolution or gyrus 13 

Inferior occipital sulcus . . . . . 13 

Inferior olivary nucleus 148 

Inferior olive 64 

Inferior parietal convolution 12 

Inferior peduncles of cerebellum (restiform body). ..102, 116, 150, 216 

Inferior rhomboid fossa 163 

Inferior sensory root of trifacial or fifth nerve 125, 143, 145 

Inferior surface of cerebellum 107, 111 

Inferior surface of cerebrum 24-51 

Inferior surface of pons 119 

Infundibulum 7, 18, 19, 214 

Inner or ependymal layer of medulla 218 

Insula 14 

Interbrain 7, 42-51, 66 

Interior of medulla 133, 149 

Interior of midbrain 54, 65 

Intermediate bundle of crusta 55, 77, 85, 86, 187 

Intermedio-lateral column of cells 168 

Internal accessory vlivary nucleus 148 

Internal arciform fibers - 135, H6 

Internal capsule 26-28, 31, 35, 36, 40, 53, 54, 55, 211 

Internal geniculate bodies 7, 49, 50, 51, 54, 57, 60, 76, 82, 215 

Internal nucleus of optic thalamus (or medial) 78 

Internal orbital convolution 22 

Interolivary fillet 62, 139, 147, 178 

Interpeduncular ganglion 57, 79 

Interpeduncular structures 18, 48 

Intraparietal fissure 12 

Intumescentia cervicalis 163 

Intumescentia lumbalis 163 

Island of Reil 10-14? 22 

Isthmus 16, 52 

Isthmus gyri fornicati iti 

Isthmus rhombencephali 

Iter a tertia ad quartum ventriculum 58 

XVII 



INDEX. 

PAGE. 

Jugular vein — internal 3 

L 

Lamina cinerea .7, 18, 31, 44, 47, 84, 214 

Lamina perforata anterior 24 

Lamina terminalis 19, 31, 43, 48 

Laminae medullares (cerebelli) 114 

Large pyramids of cerebral cortex ; 73 

function of 73 

Lateral area of medulla 140 

Lateral cerebellar veins 120 

Lateral extremity of corpus callosum 30 

Lateral fillet (or lower) 60, 63, 83, 120, 122, 139 

Lateral horn (of cord) 166 

Lateral nucleus of medulla 140 

Lateral recesses of fourth ventricle 114, 133, 151 

Lateral sinus 2 

Lateral surface of medulla 131, 132 

Lateral sulcus of midbrain 54 

Lateral tract of medulla 131 

Lateral ventricles 31, 33, 34-42 

Lateral white column of cord 167, 169 

Lemniscus 50, 123, 124 

Lemniscus interolivaris (L. medialis, L. superior) 62, 139 

Lemniscus lateralis 60, 62, 63, 120, 123, 139 

Lemniscus medialis 56, 62, 63, 120, 123, 139 

Lemniscus superior 62, 123, 139 

Lenticular nucleus 25, 26, 36, 37 

Lesions of acustic radiations 9 

Lesions of anterior corner 167 

Lesions of anterior quadrigeminal bodies 83 

Lesions of association centers 72 

Lesions of corpus striatum 77 

Lesions of cortical fillet 90 

Lesions of lower motor neurones 180 

Lesions of medulla 149 

Lesions of motor and sensory cortex 72 

Lesions of motor tracts (upper) 89 

XVIII 



INDEX. 

PAGE. 

Lesions of olfactory tract, or cortex 75 

Lesions of pons 127 

Lesions of posterior column of cord 179 

Lesions of posterior quadrigeminal bodies 83 

Lesions of posterior roots of spinal nerves 182 

Lesions of pyramidal tract 177 

Lesions of sensory paths 193 

Lesions of special sense paths 193 

Lesions of trochlear and oculomotor nuclei 84 

Ligamentum denticulatum 160 

Ligula 133 

Limbic lobe 16, 17 

Lingula and traenula of cerebellum 105 

Lissauer's tract 177 

Lobes of cerebellum, inferior surface 108-111 

Lobes of cerebellum, superior surface 105-107 

Lobes and convolutions of cerebrum, convex surface 11-14 

Lobes and convolutions of cerebrum, inferior surface 2t, 24 

Lobes and convolutions of cerebrum, medial and tentorial sur- 
face 16, 17 

Lobulus biventer 110 

Lobulus paracentralis 11. 17 

Lobulus parietalis superior, inferior. 12 

Lobulus semilunaris inferior 107 

Lobulus semilunaris superior 110 

Lobus cacuminis 106 

Lobus centralis (cerebelli) 105 

Lobus cliyi 106 

Lobus culminis 106 

Lobus frontalis 11 

Lobus lingulae 105 

Lobus noduli 109 

Lobus occipitalis 13 

Lobus olfactorius 23 

Lobus orbitalis '21 

Lobus parietalis \'2 

Lobus pyramidalis 110 

Lobus quadrangularis 106 

\i\ 



INDEX. 

PAGE 

Lobus temporalis 13 

Lobus tuberis 110 

Lobus uvulae 109 

Location of Rolandic fissure 10 

Location of Sylvian fissure 10 

Locomotor ataxia 179, 182 

Locus coeruleus 151, 152 

Loewenthal's column 174 

Long association fibers of cerebrum 92 

Long sensory tract (Ciagliniski) 171 

Longitudinal fibers of cord 172, 179, 222 

Longitudinal fibers of medulla 137-146 

Longitudinal fibers of pons. 122, 125 

Longitudinal sinus, inferior 2 

Longitudinal sinus, superior 2 

Longitudinal striae, lateral 30 

Longitudinal striae, medial 29 

Longitudinal tract of cord 172-179, 222, 223 

Lower, or closed, medulla > 142 

Lumbar enlargement of cord 163 

Lymph spaces of cerebellum 118 

Lymph spaces of cerebrum 99 

Lymph spaces of spinal cord 184 

Lyre 32, 91 

M 

Mantle (or middle) layer of embryo 205 

Mantle layer of medulla 218, 219 

Mantle layer of spinal cord .221, 222 

Marginal convolution . : , 17 

Marginal tract of Lissauer 177 

Massa intermedia 43, 48, 84 

Medial cerebral veins 98 

Medial fillet 56, 63, 83, 139 

Median sulcus of midbrain 53, 54 

Medulla oblongata 7, 128-149 

Medulla spinalis 168 

Medullary stem of cerebellum 101-103, 114- 116 

xx 



INDEX. 

page. 

Medulli-spinal veins 160, 161, 183 

Membranes of brain 1-6 

Membranes of spinal cord 159-161 

Meninges encephali 1 

Meninges of brain 1-6 

Meninges of cord 159-161 

Meningo-rachidian .4, 159, 184 

Mesencephalon 7, 52, 205, 214, 215 

Metathalamus 49 

Metencephalon 7, 129, 205, 217-219 

Methods of locating tracts of cord , 172 

Meynert's commissure 81, 84 

Midbrain 7, 52-99 

Middle association center 72 

Middle cerebral artery 95 

Middle cerebral vein 99 

Middle commissure of cerebrum 7, 48, 84 

Middle frontal convolution 11 

Middle horn of lateral ventricle (descending) 39 

Middle longitudinal fibers of pons 123-125 

Middle occipital convolution or gyrus 13 

Middle occipital sulcus 

Middle peduncle of cerebellum 103, 115, 216 

Middle transverse fibers of pons 121 

Micturition center 168 

Mitral neurones 74 

Mixed tracts of cords, ascending and descending 172, 173 

Motor areas of cerebral cortex 12, 71, 72 

Motor centers of medial surface of cerebrum 17 

Motor fibers of internal capsule 27, 85-89 

Motor fibers to arm 55, S T 

Motor fibers to head 55, 56, >7 

Motor fibers to leg and foot 56, 88 

Motor fibers to trunk 56, B8 

Motor head area 70 

Motor lower extremity area 70 

Motor memories 71 

Motor nuclei of cranial nerves 55; 56, 87, 156, 157 

\\i 



INDEX. 

PAGE. 

Motor oculi or third cranial nerve 20, 53, 58, 59, 140 

Motor or efferent paths 185-190 

Motor projection fibers of cerebrum . . : 85-89 

Motor projection fibers to cranial nerves 87 

Motor speech center 12, 70, 93 

Motor trunk area 70 

Motor upper extremity area 70 

Motor writing center. 70 

Myelencephalon 7, 205 

Myelospongium , 205 



Naming center 71 

Nerve supply of membranes of cord 161 

Nerves of dura mater 4 

Nerves of Lancisi 17, 29, 30 

Nerves of pia 6 

Nervi olfactorii 23, 154 

Nervus opticus 21, 154 

Nervus abducens 155 

Nervus accessorius 156 

Nervus acusticus 144, 155 

Nervus cochlearis 120 

Nervus facialis 155 

Nervus glassopharyngeus 156 

Nervus hypoglossus 137, 156 

Nervus intermedins 155 

Nervus oculomotorius 20, 154 

Nervus trigeminus 120, 155 

Nervus trochlearis 20, 59, 154 

Nervus vagus 156 

Neural crest 202-204 

Neural tube 204-224 

Neuraxones (or axones) 67 

Neuroblasts 204 

Neuroglia , 67, 205 

Neurogliar layer of medulla 219 

Neuron 68 

XXII 



INDEX 

PAGE. 

Neurone 66 

Neurone center (cell body ) 65 

Neurones of cajal 72 

Ninth nerve 131 

Nodulus and flocculi 109 

Nodulus vermis 109 

Note on the neurone 68 

Nuclei of cranial nerves (ventral series) 156 

Nuclei of cranial nerves (dorsal series) 156 

Nuclei of optic thalamus 78 

Nuclei of pons '. .55, 56, 122, 126, 216 

Nuclei of Stilling 113 

Nuclei of Stilling (in cord) , 169 

Nucleus accessorius dorsalis 148 

Nucleus accessorius medialis 148 

Nucleus ambignus 140, 146 

Nucleus amygdalae 37 

Nucleus arcuatus 149 

Nucleus candatus (see candate nucleus) 37 

Nucleus cuneatus 62, 136, 143, 147, 219 

Nucleus dentatus 113 

Nucleus dorsalis 168 

Nucleus emboliformis 113 

Nucleus fastigii 114 

Nucleus globosus 113 

Nucleus gracilis : 62, 136, 143, 147, 219 

Nucleus hypothalamicus 50, 57, 81 

Nucleus lentiformis 36 

Nucleus magno-cellularis 127 

Nucleus of abducent, or sixth cranial nerve 145, 152, 216, 219 

Nucleus of external arciform fibers 149 

Nucleus ot facial, or seventh cranial nerve 216 

Nucleus of fifth nerve (inferior) 117 

Nucleus of formatio reticularis 126 

Nucleus of glossopharyngeal, or ninth nerve 153 

Nucleus of habenula 7s 

Nucleus of lateral fillet 63, 122 

Nucleus of Luys (Luysi) 50, 57, 76, 81, SI 

win 



INDEX. 

PAGE. 

Nucleus of ninth, tenth'and eleventh cranial nerves 146, 147, 219 

Nucleus of pneumogastric, or tenth nerve 153 

Nucleus of pons (see nucleus pontis). 55, 56 

Nucleus of pulvinar 78 

Nucleus of Rolando 143, 219 

Nucleus of superior olive 63, 122, 126, 216 

Nucleus of third and fourth nerves 58, 59, 84, 215 

Nucleus of trapezium 121, 122, 126 

Nucleus of trapezoid body 63 

Nucleus of trifacial, or fifth nerve (motor) 152, 216 

Nucleus of twelfth, or hypoglossal, cranial nerve 146, 219 

Nucleus olivaris (medullae) 148 

Nucleus olivaris superior 126 

Nucleus pontis 55, 56, 122, 126, 216 

Nucleus ruber 50, 57, 81 

O 

Obex 133 

Occipital lobe 13 

Occipital sinus 2 

Oculomotor groove 53 

Oculomotor nerve 154 

Oculomotor nucleus 58 

Olfactory bulb , 22, 74 

Olfactory conduction paths 75, 194 

Olfactory lobes 7, 22, 208 

Olfactory nerve 154 

Olfactory tract. 22, 23 

Olfactory trigone 22, 24 

Olivary body (of medulla) 131, 219 

Olivary bundle of spinal cord 148 

Olivary fasciculus 64, 77,124, 141 

Olivary nucleus external accessory 140 

Olivary nucleus internal accessory 140 

Olivary nucleus of medulla 140, 148 

Olivary peduncle 136 

Operculum : •. 10, 12 

orbital. 10 

XXIV 



INDEX. 

PAGE. 

frontal 10 

fronto-parietal 10, 12 

Optic chiasm or commissure 18, 20 

Optic conduction path 194, 195 

Optic lobes 82 

Optic nerve 154 

Optic radiations 80 

Optic recess 48 

Optic thalamus (i) 7, 26, 31, 35, 37, 44,48, 76, 78-81, 214 

Optic tracts and commissure 7, 18, 44 

Optic vesicle 213 

Orbital lobe 21 

Orders of neurones 68 

Origin of cranial and spinal ganglia 202, 203 

Origin of cranial nerves 153-158 

Origin of medulla 129 

Origin of meninges 202 

Origin of neurones 204 

Origin of optic nerves, chiasm and tracts 213 

Origin of spinal cord 162 

P 

Pacchionian bodies 3 

Paracentral lobule 11, 17 

Parietal lobe 12 

Parieto-occipital fissure 11, 15 

Pars anterior commissurae anterioris 47 

Pars anterior lobuli quadrangularis 106 

Pars basilaris pontis 119, 121 

Pars dorsalis-pontis 119. 121. 122 

Pars frontalis capsulae internae 27 

Pars intermedia • 155 

Pars occipitalis capsulae internae 27 

Pars posterior commissurae anterioris 47 

Pars posterior lobuli quadrangularis 106 

Parturition center 168 

Pedes pedunculi (see crustae) 7 

Peduncle of flosculus 108 

\\\ 



INDEX. 

PAGE. 

Pedunculus cerebri (see midbrain) 7 

Pedunculus flocculi 109 

Perikaryon (or neurone center) 66, 167, 168 

Permanent fissures of cerebrum 209, 210 

Perpendicular fasciculus 94 

Pes hippocampi 40, 41 

Petrosal sinuses, inferior and superior 3, 99, 118 

Pia mater encephali 5 

Pia mater of brain 5 

Pia mater of spinal cord 160 

Pia mater spinalis 5, 160 

Pillars of fornix 20, 32, 210, 211 

Pineal body 7, 31, 43, 45, 214 

Pineal stalk 45 

Pineal striae 46 

Pituitary body 18, 19 

Plexus choroideus ventriculi quarti 38, 133, 153 

Plexus choroideus ventriculi tertii. 45, 47 

Plexus venosi vertebrales interni 159, 184 

Pneumogastric or vagus nerve 130, 131, 156, 157 

Pneumogastric trigone 153 

Points of difference between dura of brain and cord 4 

Polymonphous layer of cortex 73 

function of 73 

Pons varolii 7, 118-127 

Ponticulus of Arnold 130 

Postcentral convolution or gyrus 11 

Postcentral fissure (of cerebellum) 104 

Postcentral fissure or sulcus 12 

Postclival fissure 104 

Postnodular fissure 107 

Postparietal convolution 12 

Postpyramidal fissure 108 

Posterior association center 71 

Posterior area of medulla 142-146 

Posterior brachium 51, 83, 90, 215 

Posterior cerebellar notch 101 

Posterior cerebral arteries 95, 96 

XXVI 



INDEX. 

PAGE 

Posterior choroid tela ( or inferior) 6, 133 

Posterior communicating arteries 95 

Posterior commissure of cerebrum 7, 31, 42, 43, 44, 53, 214 

Posterior commissure of cord 165, 169 

Posterior cornu in medulla 147 

Posterior cornu of cord 166, 1 69, 171 

Posterior cornu (or horn) of lateral ventricle 39 

Posterior crescentic lobules of cerebellum 106 

Posterior fenestrated septum 160 

Posterior inferior cerebellar artery 117 

Posterior intermediate furrow 165 

Posterior longitudinal bundle 50, 61, 124, 139, 140, 173, 174 

Posterior median fissure of medulla 128 

Posterior median fissure of cord 164, 223 

Posterior nucleus of optic thalami 78 

Posterior olfactory lobule 22, 24 

Posterior orbital convolution 22 

Posterior perforated lamina (or space) 31, 44, 53 

Posterior quadrigeminal body 63, 76 83 

Posterior root of spinal nerves 180, 182 

Posterior sclerosis 179 

Posterior segment of internal capsule 27 

Posterior spinal artery 161, 182, 183 

Posterior white column of cord 169 

Postero-inferior lobules of cerebellum 110 

Postero-lateral choroid artery 38, 97 

Postero-lateral fissure of cord 164, 223 

Postero-lateral ganglionic arteries 97 

Postero-lateral tract of cord 177, 178 

Postero-medial choroid artery 98 

Postero-medial tract of cord 179 

Poslero-median ganglionic arteries 97 

Postero-superior lobules of cerebellum I0t> 

Precentral convolution 11 

Precentral fissure, or sulcus, of cerebellum UM 

Precentral fissure, or sulcus, of cerebrum II 

Preclival fissure HM 

Prepyramidal fissure 108 

x \ V 1 1 



INDEX. 

PAGE. 

Primary brain vesicles 204 

Primary sulci of cerebrum 209 

Processus reticularis 166 

Projection or peduncular fibers 'of cerebellum 114-116 

Projection or peduncular fibers of cerebrum 85-91 

Prosencephalon 7,9, 205, 207, 208-213 

Pulvinar of optic thalamus 40, 41, 49, 90 

Pupillary reflex 200 

Pupillo-dilator tract 124, 140 

Putamen 36 

Pyramid and digastric lobules 110 

Pyramid of medulla 1.30, 138 

Pyramidal conduction paths 185, 186 

Pyramidal tract 27, 55, 86, 89, 122 

Py ramis medull ae oblongatae 138 

Pyramis vermis 110 

Q 

Quadrate lobe *. 17 

Quadrigeminal bodies 57, 82, 83 

Quadrigeminal lamina 60 

Qualities pecular to axones 68 

Qualities peculiar to dendrites 68 

R 

Radiatio occipito-thalamica (Gratioleti)l 28, 80 

Radiatio temporo-thalamica 28, 81 

Radix anterior (nervi spinalis) 180 

Radix cerebralis nervi accessorii 137 

Radix medialis lateralis (nervi optici) 21 

Radix nervi glossopharyngei 137 

Radix nervi vagi 137 

Radix nervi vestibularis 137 

Radix posterior (nervi spinalis) 180 

Radix spinalis nervi trigemini 145 

Raphe (of medulla) .- 135 

Real central terminations of posterior spinal roots 181 

Recessus lateralis ventriculi quarti 114 

XXVIII 



INDEX. 

PAGE. 

Red nucleus 50, 57, 64, 81 

Reflex centers of cord 168 

Reflex paths 198, 201 

Region of speech •. . 12, 70 

Respiratory reflex 200 

Restiform body 132, 133, 143, 144, 219 

Reticula of cord 166 

Rhinencephalon 17, 93 

Rolandic nucleus 132 

Roof epithelium of fourth ventricle 133, 151 

Roof epithelium of third ventricle r 31, 43, 44 

Roots of auditory nerve 144 

Roots of olfactory tract 23 

Roots of optic tract 21,51 

Roots of spinal nerves 179, 182 

Root veins 183 

Rostrum of corpus callosum 30, 39 



Second temporal convolution or gyrus 14 

Second temporal fissure or sulcus 13 

Secondary brain vesicles 205 

Secretory centers 168 

Sensory areas of cerebrum 70 

Sensory conduction paths 190-197 

Sensory decussation 62, 136, 147, 219 

.Sensory fibers of internal capsule 27. 89-91 

Septomarginal tract 118, 170 

Septum lucidum 31, 33. 35, 39 211 

Septum pellucidum 33 

Septum subarachnoideale 160 

Seventh cranial nerve (facial) 124 

Short association fibers of cerebrum 91 

Sinus basilaris 3 

Sinus cavernosus . . 3 

Sinus circularis 3 

Sinus occipitalis 2 

Sinus petrosus superior et inferior 3 

XXIX 



INDEX. 

PAGE. 

Sinus rectus .' 2 

Sinus sagittalis superior and inferior 2, 98, 99 

Sinuses of dura mater 2, 3 

Sixth cranial nerve (abducent) 61, 124 

Sixth ventricle 162 

Small pyramids of cerebral vortex 72 

functions of 73 

Solitary bundle 145, 218 

Somaesthetic area 13, 26, 28, 70 

Special-sense conduction paths 194-197 

Spinal accessory nerve 156 

Spinal and cranial reflexes 199, 200 

Spinal bulb 128 

Spinal cord 162-184, 220-224 

Spinal cord in foetus 162 

Spinal ganglion 181, 203 

Spinal reflexes 198, 199 

Spinal root of trifacial (or fifth) nerve 143 

Splenium of corpus callosum 29, 31 

Spongioblasts 205 

Stellate cells of cerebellum Ill 

Strabismus 127 

Straight sinus 2 

Stratum cmereum 82 

Stratum dorsale hypothalami 50, 64 

Stratum glomerulosum 74 

Stratum lemnisci 82 

Stratum opticum 82 

Stratum zonale 49, 82 

Stria medullaris thalami 46 

Stria terminalis 37 

Striae longitudinales laterales et mediales 29, 30 

Striae medullares 151 

Striae olfactorii lateralis, medialis, intermedia 23 

Subarachnoid spaces 5, 160, 161 

Subarachnoid tissue 4 

Substance of spinal cord 160-182 

Substantia alba (of cord) 171-182 

xxx 



INDEX. 

PAGE. 

Substantia cinerea gelatinosa Rolandi 166 

Substantia gelatinosa Rolandi 166 

Substantia grisea 165 

Substantia intermedia grisea . 166, 168 

Substantia nigra 7, 50, 54, 56, 57, 66, 76, 83 

Substantia perforata posterior 53, 57 

Substantia spongiosa 166 

Sulcus ( i) centralis 10 

Sulcus centralis insulae 14 

Sulcus cinguli 15 

Sulcus circularis (Reili) 14, 22 

Sulcus frontalis superior et inferior 11 

Sulcus horizontalis cerebelli 101 

Sulcus interparietalis 12 

Sulcus intermedius posterior (of cord) 165 

Sulcus (i) lateralis (mesencephali) 53 

Sulcus lateralis anterior (medullae)„ 129 

Sulcus lateralis posterior (medullae). 130 

Sulcus lateralis posterior (of cord) 165 

Sulcus limitans insulae 14, 22 

Sulcus longitudinalis fossae rhomboideae 151 

Sulcus mediana anterior (of cord) 163 

Sulcus mediana posterior (of cord) 164 

Sulcus nervi oculomotorii 53 

Sulcus occipitalis (es) lateralis (es) 13 

Sulcus occipitalis (es) transversus 13 

Sulcus occipito-parietalis 11, 15 

Sulcus olf actorius 2'2 

Sulcus postcentralis 12 

Sulcus postcentralis cerebelli 104 

Sulcus praecentralis 11 

Sulcus praecentralis cerebelli 104 

Sulcus temporalis superior et medius 11 

Superficial longitudinal fibers of pons 125 

Superficial, molecular, or gray cellular layer Ill 

Superficial, molecular, or neurogliar layer of cortex 72 

Superficial origin of anterior root of spinal nerves 180 

Superficial origin of posterior root of spinal nerves 181 

XXXI 



INDEX. 

PAGE. 

Superior cerebellar artery 117 

Superior cerebellar veins 118 

Superior cerebral veins 98 

Superior fillet 63, 139 

Superior fovea 151, 152, 218 

Superior frontal convolution or gyrus 11 

Superior frontal fissure or sulcus 11 

Superior lamina of internal capsule 26, 53, 54, 211 

Superior lamina of medullary stem 102, 114 

Superior longitudinal fasciculus 93 

Superior medullary velum 102, 115, 120 

Superior occipital convolution 13 

Superior occipital fissure or sulcus 13 

Superior olivary nucleus 126, 216 

Superior parietal convolution 11 

Superior peduncle of cerebellum 

50, 60, 64, 88, 102, 114, 115, 116, 120, 125, 150, 216 

Superior surface-of cerebellum. . .• 103-106 

Superior surface of pons 119 

Supramarginal convolution 12 

Surfaces of corpus callosum 29 

Surfaces of medulla 129-133 

Surfaces of midbrain 52-54 

Surfaces of optic thalamus 49 

Surfaces of pons 119-120 

Surfaces of spinal cord 163 

Surcingle 37, 40 

Sustentacular tissue of brain and cord 67 

Sylvian fissure 10, 209, 210 

T 

Table I 6 

Table II 154, 156 

Table III 207-208 

Taeniae tectae 30 

Taenia semicircularis 31, 35, 37, 40, 211 

Tail of candate nucleus 37 

Tangential association of fibers of cerebrum 91 

XXXII 



INDEX. 

PAGE. 

Tapetum 94 

Tegmentum 7, 31, 40, 50, 54, 57, 65, 66, 215 

Tela choroidea ventriculi quarti 6, 133 

Tela choroidea ventriculi tertii 5, 44, 46, 213 

Telencephalon 205 

Temporal lobe 13 

Temporo-pontal tract 26, 27, 86 

Tenth nerve '. 131 

Tent of fourth ventricle 114, 151 

Tentorium cerebelli 2, 9 

Terminal nuclei of sensory cranial nerves 62, 153, 157 

Thalamencephalon 7, 205, 213, 214 

Thalamus 37, 48, 78-80 

Three systems of Flechsig 89 

Third cranial nerve. 53, 61, 124, 140 

Third temporal convolution 14 

Third ventricle 31, 33, 42 

Third ventricle and interbrain 42-51 

Time of medullation of tracts of cord 222 

Tonsila cerebelli 109 

Tonsil or amygdala of cerebellum 109 

Torcular Herophili 2 

Tracing of impulses 185-201 

Tract from lateral nucleus to cerebellum 116, 132, 144 

Tracts of antero-lateral column 172 

Tracts of posterior column of cord 177, 179 

Tractus cerebro-corticopontalis, frontalis (see fronto-pontal) 27 

Tractus cerebo-corticopontalis, temporales (see temporo-pontal). 

27. 85. 86 

Tractus olfactorius 23 

Tractus opticus - 1 

Tractus triangularis (Helwigi) 141 

Tractus spinalis nervi trigemini 125 

Transverse fibers of cord 171, 17'J 

Transverse fibers of medulla 136 

Transverse fibers of pons 121, 122 

Transverse or basilar sinus 3 

Transverse or commissural fibers of cerebrum B5, l .'l 

XXXII] 



INDEX. 

PAGE. 

Trapezium 121, 122 

Triangular tract of Helwig 124, 141, 148, 175 

Trifacial nerve 155 

Trigone and area of Broca (olfactory) 24 

Trigone of habenula 50 

Trigonum acustici 152, 153 

Trigonum collaterale 40 

Trigonum habenulae 50, 79 

Trigonum nervi hypoglossi 152 

Trigonum olfactorium 24 

Trigonum vagi 152, 153 

Trigonum ventriculi 39, 40 

Tri-radiate or H shaped fissure 22 

Trochlear nerve 154 

Trochlear nucleus (pathetic) 58 

Tuber annulare 119 

Tuber cinereum and infundibulum 7, 18, 31, 44, 84, 214 

Tuberculum anterius thalami 50 

Tuberculum cuneatum 147 

Tuber valvula and postero-inferior lobules 110 

Tuber vermis 110 

Turcks' column 174 

Types of neurones 68 

Typical cortex of cerebrum 72 

U 

Uncinate convolution 17 

Uncinate fasciculus ." 93 

Uncrossed (or direct) pyramidal tract 138, 174 

Uncrossed pyramidal fibers 138 

Upper, or ventricular, medulla 144 

Uvula and tonsils 109 

Uvula vermis 109 

V 

Vagus, or pneumogastric nerve 130, 137, 153, 156, 157 

Vallecula cerebelli 101, 107 

Vallecula Sylvii 10, 2T 

XXXIV 



INDEX. 

PAGE. 

Valley of cerebellum 101 

Valve of Vienssens 58, 64, 102, 120, 125, 150 

Varieties of reflex paths 198 

Vasomotor centers 168 

Vein of Galen 98 

Veins, internal jugular 3 

Veins, medulli-spinal 160, 161, 183 

Veins, meningo-rachidian 4 

Veins of cerebellum 118 

Veins of cerebrum 98 

Veins of pia 6 

Veins of spinal cord 183, 184 

Veins of striate body 98 

Velum interpositum 5, 9, 31, 38, 43, 46, 212, 213 

Velum medullare anterius 64, 102, 115, 120, 127, 130 

Velum medullare posterius 101, 114 

Vena cerebri interna 38 

Vena cerebri magna (Galeni) 2, 38, 98, 99 

Vena cerebri media 99 

Vena choroidea 98 

Vena corpora striati 98 

Venae cerebri inferiores 98 

Venae cerebri internae 9S 

Venae cerebri mediales 98 

Venae cerebri superiores 98 

Venae spinales externae 160, 161, 183 

Ventral deep-longitudinal fibers of pons 122 

Ventral deep-transverse fibers of pons 121 

Ventral longitudinal fibers of pons 122 

Ventral surface of medulla 130 

Ventral surface of pons 1 19 

Ventral transverse fibers of pons 121 

Ventral zone of embryo 205, 214, 215, 217. 219, 220 

Ventricle of corpus callosum 30 

Ventriculus lateralis 31 

Ventriculus lateralis (pars centralis) 36 

Ventriculus quartus 100, 1 50 

Ventriculus tertius 42 



SEP 151902 

1C0P> DEL i 
SEP. 15 1902 



INDEX. 



PAGE. 

Ventro-lateral groove of medulla 129 

Vermis cerebelli 100, 101 

Vermis inferior cerebelli 101 

Vermis superior cerebelli 101 

Vestibular nuclei of auditory nerve 144, 153 

Vestibulo-olivary -tract. 148 

Villi of arachnoid 4 

Vinculum linguae cerebelli 105 

Visceral centers 168 

Visual center 71 

Visual conduction paths 90 

Visual memory center 13, 71, 93 

W 

Waldeyer's column of cells 168, 169 

Wallerian degeneration 68 

White matter of brain and cord 67 

White matter of cerebellum 114-117 

White matter of cerebrum and midbrain 85-94 

White matter of medulla 134-146 

White matter of pons 120-125 

White matter of spinal cord 171-182 

White matter of thalamus , 79 

White or anterior commissure of cord 171 

Worm of cerebellum 100, 101 

Z 
Zona incerta 50 



